[ENHANCEMENT+CLEANUP] Better compile time errors for strict mode

Removing support for implicit this fallback {{foo}} -> {{this.foo}}

When a strict mode template references an undefined variable, it
really should produce a compile-time error, arguably that is the
point of the feature.

However, it seems like previously a lot of these errors ended up
propagating and is actually handled by the runtime compiler.

The original/primary goal here started out as cleaning up all the
code for implicit this fallback, but as I delete code it eventually
revaled all the places where strict mode was inappropiately using
the same infrastructure ("unresolved free variables", which isn't
really a sensible thing).

Also:

* Removes `{{#with}}`
* Removes "deprecated call" @foo={{bar}}
* Removes unused opcodes
* Syncs keyword list with Ember

packages/@glimmer-workspace/integration-tests/lib/suites/components.ts

@@ -268,7 +268,7 @@ export class GlimmerishComponents extends RenderTest {
   })
   'invoking dynamic component (local) via angle brackets'() {
     this.registerComponent('Glimmer', 'Foo', 'hello world!');
-    this.render(`{{#with (component 'Foo') as |Other|}}<Other />{{/with}}`);
+    this.render(`{{#let (component 'Foo') as |Other|}}<Other />{{/let}}`);
 
     this.assertHTML(`hello world!`);
     this.assertStableRerender();
@@ -280,7 +280,7 @@ export class GlimmerishComponents extends RenderTest {
   'invoking dynamic component (local path) via angle brackets'() {
     this.registerHelper('hash', (_positional, named) => named);
     this.registerComponent('Glimmer', 'Foo', 'hello world!');
-    this.render(`{{#with (hash Foo=(component 'Foo')) as |Other|}}<Other.Foo />{{/with}}`);
+    this.render(`{{#let (hash Foo=(component 'Foo')) as |Other|}}<Other.Foo />{{/let}}`);
 
     this.assertHTML(`hello world!`);
     this.assertStableRerender();
@@ -291,7 +291,7 @@ export class GlimmerishComponents extends RenderTest {
   })
   'invoking dynamic component (local) via angle brackets (ill-advised "htmlish element name" but supported)'() {
     this.registerComponent('Glimmer', 'Foo', 'hello world!');
-    this.render(`{{#with (component 'Foo') as |div|}}<div />{{/with}}`);
+    this.render(`{{#let (component 'Foo') as |div|}}<div />{{/let}}`);
 
     this.assertHTML(`hello world!`);
     this.assertStableRerender();
@@ -302,7 +302,7 @@ export class GlimmerishComponents extends RenderTest {
   })
   'invoking dynamic component (local) via angle brackets supports attributes'() {
     this.registerComponent('Glimmer', 'Foo', '<div ...attributes>hello world!</div>');
-    this.render(`{{#with (component 'Foo') as |Other|}}<Other data-test="foo" />{{/with}}`);
+    this.render(`{{#let (component 'Foo') as |Other|}}<Other data-test="foo" />{{/let}}`);
 
     this.assertHTML(`<div data-test="foo">hello world!</div>`);
     this.assertStableRerender();
@@ -313,7 +313,7 @@ export class GlimmerishComponents extends RenderTest {
   })
   'invoking dynamic component (local) via angle brackets supports args'() {
     this.registerComponent('Glimmer', 'Foo', 'hello {{@name}}!');
-    this.render(`{{#with (component 'Foo') as |Other|}}<Other @name="world" />{{/with}}`);
+    this.render(`{{#let (component 'Foo') as |Other|}}<Other @name="world" />{{/let}}`);
 
     this.assertHTML(`hello world!`);
     this.assertStableRerender();
@@ -324,7 +324,7 @@ export class GlimmerishComponents extends RenderTest {
   })
   'invoking dynamic component (local) via angle brackets supports passing a block'() {
     this.registerComponent('Glimmer', 'Foo', 'hello {{yield}}!');
-    this.render(`{{#with (component 'Foo') as |Other|}}<Other>world</Other>{{/with}}`);
+    this.render(`{{#let (component 'Foo') as |Other|}}<Other>world</Other>{{/let}}`);
 
     this.assertHTML(`hello world!`);
     this.assertStableRerender();
@@ -351,7 +351,7 @@ export class GlimmerishComponents extends RenderTest {
       Foo
     );
     this.render(
-      `{{#with (component 'Foo') as |Other|}}<Other @staticNamedArg="static" data-test1={{this.outer}} data-test2="static" @dynamicNamedArg={{this.outer}}>template</Other>{{/with}}`,
+      `{{#let (component 'Foo') as |Other|}}<Other @staticNamedArg="static" data-test1={{this.outer}} data-test2="static" @dynamicNamedArg={{this.outer}}>template</Other>{{/let}}`,
       { outer: 'outer' }
     );
 

packages/@glimmer-workspace/integration-tests/lib/suites/debugger.ts

@@ -75,7 +75,7 @@ export class DebuggerSuite extends RenderTest {
     });
 
     this.render(
-      '{{#with this.foo as |bar|}}{{#if this.a.b}}true{{debugger}}{{else}}false{{debugger}}{{/if}}{{/with}}',
+      '{{#let this.foo as |bar|}}{{#if this.a.b}}true{{debugger}}{{else}}false{{debugger}}{{/if}}{{/let}}',
       expectedContext
     );
     this.assert.strictEqual(callbackExecuted, 1);

packages/@glimmer-workspace/integration-tests/lib/suites/scope.ts

@@ -9,11 +9,11 @@ export class ScopeSuite extends RenderTest {
   'correct scope - conflicting local names'() {
     this.render({
       layout: stripTight`
-        {{#with @a as |item|}}{{@a}}: {{item}},
-          {{#with @b as |item|}} {{@b}}: {{item}},
-            {{#with @c as |item|}} {{@c}}: {{item}}{{/with}}
-          {{/with}}
-        {{/with}}`,
+        {{#let @a as |item|}}{{@a}}: {{item}},
+          {{#let @b as |item|}} {{@b}}: {{item}},
+            {{#let @c as |item|}} {{@c}}: {{item}}{{/let}}
+          {{/let}}
+        {{/let}}`,
       args: { a: '"A"', b: '"B"', c: '"C"' },
     });
 
@@ -25,7 +25,7 @@ export class ScopeSuite extends RenderTest {
   'correct scope - conflicting block param and attr names'() {
     this.render({
       layout:
-        'Outer: {{@conflict}} {{#with @item as |conflict|}}Inner: {{@conflict}} Block: {{conflict}}{{/with}}',
+        'Outer: {{@conflict}} {{#let @item as |conflict|}}Inner: {{@conflict}} Block: {{conflict}}{{/let}}',
       args: { item: '"from block"', conflict: '"from attr"' },
     });
 

packages/@glimmer-workspace/integration-tests/test/ember-component-test.ts

@@ -372,14 +372,14 @@ class CurlyScopeTest extends CurlyTest {
       stripTight`
         <div>
           [Outside: {{this.zomg}}]
-          {{#with this.zomg as |lol|}}
+          {{#let this.zomg as |lol|}}
             [Inside: {{this.zomg}}]
             [Inside: {{lol}}]
             <FooBar @foo={{this.zomg}}>
               [Block: {{this.zomg}}]
               [Block: {{lol}}]
             </FooBar>
-          {{/with}}
+          {{/let}}
         </div>`,
       { zomg: 'zomg' }
     );
@@ -419,14 +419,14 @@ class CurlyScopeTest extends CurlyTest {
       stripTight`
         <div>
           [Outside: {{this.zomg}}]
-          {{#with this.zomg as |lol|}}
+          {{#let this.zomg as |lol|}}
             [Inside: {{this.zomg}}]
             [Inside: {{lol}}]
             {{#foo-bar foo=this.zomg}}
               [Block: {{this.zomg}}]
               [Block: {{lol}}]
             {{/foo-bar}}
-          {{/with}}
+          {{/let}}
         </div>`,
       { zomg: 'zomg' }
     );
@@ -991,9 +991,9 @@ class CurlyClosureComponentsTest extends CurlyTest {
 
     this.render(
       stripTight`
-        {{#with (hash comp=(component 'foo-bar')) as |my|}}
+        {{#let (hash comp=(component 'foo-bar')) as |my|}}
           {{#component my.comp arg1="World!"}}Test1{{/component}} Test2
-        {{/with}}
+        {{/let}}
       `
     );
 
@@ -1007,9 +1007,9 @@ class CurlyClosureComponentsTest extends CurlyTest {
 
     this.render(
       stripTight`
-        {{#with (hash comp=(component 'foo-bar')) as |my|}}
+        {{#let (hash comp=(component 'foo-bar')) as |my|}}
           {{#component my.comp}}World!{{/component}} Test
-        {{/with}}
+        {{/let}}
       `
     );
 
@@ -1023,9 +1023,9 @@ class CurlyClosureComponentsTest extends CurlyTest {
 
     this.render(
       stripTight`
-        {{#with (hash comp=(component 'foo-bar')) as |my|}}
+        {{#let (hash comp=(component 'foo-bar')) as |my|}}
           {{component my.comp arg1="World!"}} Test
-        {{/with}}
+        {{/let}}
       `
     );
 
@@ -1039,9 +1039,9 @@ class CurlyClosureComponentsTest extends CurlyTest {
 
     this.render(
       stripTight`
-        {{#with (hash comp=(component 'foo-bar')) as |my|}}
+        {{#let (hash comp=(component 'foo-bar')) as |my|}}
           {{component my.comp}} World!
-        {{/with}}
+        {{/let}}
       `
     );
 
@@ -1131,9 +1131,9 @@ class CurlyClosureComponentsTest extends CurlyTest {
 
     this.render(
       stripTight`
-        {{#with (hash comp=(component 'foo-bar')) as |my|}}
+        {{#let (hash comp=(component 'foo-bar')) as |my|}}
           {{my.comp}} World!
-        {{/with}}
+        {{/let}}
       `
     );
 
@@ -1190,11 +1190,11 @@ class CurlyClosureComponentsTest extends CurlyTest {
 
     this.render(
       stripTight`
-        {{#with (component "foo-bar" "outer 1" "outer 2" a="outer a" b="outer b" c="outer c" e="outer e") as |outer|}}
-          {{#with (component outer "inner 1" a="inner a" d="inner d" e="inner e") as |inner|}}
+        {{#let (component "foo-bar" "outer 1" "outer 2" a="outer a" b="outer b" c="outer c" e="outer e") as |outer|}}
+          {{#let (component outer "inner 1" a="inner a" d="inner d" e="inner e") as |inner|}}
             {{#component inner "invocation 1" "invocation 2" a="invocation a" b="invocation b"}}---{{/component}}
-          {{/with}}
-        {{/with}}
+          {{/let}}
+        {{/let}}
       `
     );
 

packages/@glimmer-workspace/integration-tests/test/helpers/array-test.ts

@@ -6,11 +6,11 @@ class ArrayTest extends RenderTest {
   @test
   'returns an array'() {
     this.render(strip`
-    {{#with (array "Sergio") as |people|}}
+    {{#let (array "Sergio") as |people|}}
       {{#each people as |personName|}}
         {{personName}}
       {{/each}}
-    {{/with}}`);
+    {{/let}}`);
 
     this.assertHTML('Sergio');
 
@@ -20,11 +20,11 @@ class ArrayTest extends RenderTest {
   @test
   'can have more than one value'() {
     this.render(strip`
-    {{#with (array "Sergio" "Robert") as |people|}}
+    {{#let (array "Sergio" "Robert") as |people|}}
       {{#each people as |personName|}}
         {{personName}},
       {{/each}}
-    {{/with}}`);
+    {{/let}}`);
 
     this.assertHTML('Sergio,Robert,');
 
@@ -34,11 +34,11 @@ class ArrayTest extends RenderTest {
   @test
   'binds values when variables are used'() {
     this.render(
-      strip`{{#with (array this.personOne) as |people|}}
+      strip`{{#let (array this.personOne) as |people|}}
             {{#each people as |personName|}}
               {{personName}}
             {{/each}}
-          {{/with}}`,
+          {{/let}}`,
       {
         personOne: 'Tom',
       }
@@ -58,11 +58,11 @@ class ArrayTest extends RenderTest {
   @test
   'binds multiple values when variables are used'() {
     this.render(
-      strip`{{#with (array this.personOne this.personTwo) as |people|}}
+      strip`{{#let (array this.personOne this.personTwo) as |people|}}
             {{#each people as |personName|}}
               {{personName}},
             {{/each}}
-          {{/with}}`,
+          {{/let}}`,
       {
         personOne: 'Tom',
         personTwo: 'Yehuda',

packages/@glimmer-workspace/integration-tests/test/modifiers/dynamic-modifiers-test.ts

@@ -134,7 +134,7 @@ class DynamicModifiersResolutionModeTest extends RenderTest {
         this.registerComponent('TemplateOnly', 'Bar', '<div {{x.foo}}></div>');
       },
       syntaxErrorFor(
-        'You attempted to invoke a path (`{{#x.foo}}`) as a modifier, but x was not in scope. Try adding `this` to the beginning of the path',
+        'You attempted to invoke a path (`{{x.foo}}`) as a modifier, but x was not in scope',
         '{{x.foo}}',
         'an unknown module',
         1,