The big ESM migration commit.

Refs #33.

This updates `@rules_prerender` to use ESM modules everywhere. This makes a few changes throughout the workspace:
1. Renames `*.{ts,js}` -> `*.{mts,mjs}`.
2. Updates imports to include `.mjs` in the file path.
3. Updates any hard-coded CommonJS `require()` or `module.exports` to use ESM syntax.
4. Updates `tsconfig.json` files to use `module: "ES2020"` and `moduleResolution: "node"`.
5. Updates `package.json` files to use `type: "module"`.

Most of the changes are fairly mechanical syntax modifications, though there are a couple random edits thrown in as necessary to switch over to ESM.

Most of this was generated by running:

```
$ echo {common,examples,packages,tools}/**/*.ts | tr " " "\n" | xargs -I {} bash -c "git mv {} \$(echo {} | sed 's,\\.ts$,.mts,g')"
$ sed -i -E "s,^import (.*?) from '(\..*?)';,import \1 from '\2.mjs';,g" {common,examples,packages,tools}/**/*.mts
$ sed -i -E "s,^export (.*?) from '(\..*?)';,export \1 from '\2.mjs';,g" {common,examples,packages,tools}/**/*.mts
$ sed -i "s,\\.ts\",.mts\",g" {.,common,examples,packages,tools}/**/BUILD.bazel
$ sed -i "s,\\.js\",.mjs\",g" {.,common,examples,packages,tools}/**/BUILD.bazel
```

common/BUILD.bazel

@@ -6,14 +6,14 @@ load(":paths_test.bzl", "paths_test_suite")
 
 ts_project(
     name = "binary",
-    srcs = ["binary.ts"],
+    srcs = ["binary.mts"],
     visibility = ["//visibility:public"],
     deps = ["//:node_modules/@types/node"],
 )
 
 ts_project(
     name = "binary_test_lib",
-    srcs = ["binary_test.ts"],
+    srcs = ["binary_test.mts"],
     testonly = True,
     deps = [
         ":binary",
@@ -28,13 +28,13 @@ jasmine_node_test(
 
 ts_project(
     name = "collections",
-    srcs = ["collections.ts"],
+    srcs = ["collections.mts"],
     visibility = ["//visibility:public"],
 )
 
 ts_project(
     name = "collections_test_lib",
-    srcs = ["collections_test.ts"],
+    srcs = ["collections_test.mts"],
     testonly = True,
     deps = [
         ":collections",
@@ -49,13 +49,13 @@ jasmine_node_test(
 
 ts_project(
     name = "formatters",
-    srcs = ["formatters.ts"],
+    srcs = ["formatters.mts"],
     visibility = ["//visibility:public"],
 )
 
 ts_project(
     name = "formatters_test_lib",
-    srcs = ["formatters_test.ts"],
+    srcs = ["formatters_test.mts"],
     testonly = True,
     deps = [
         ":formatters",
@@ -70,14 +70,14 @@ jasmine_node_test(
 
 ts_project(
     name = "file_system",
-    srcs = ["file_system.ts"],
+    srcs = ["file_system.mts"],
     visibility = ["//visibility:public"],
     deps = ["//:node_modules/@types/node"],
 )
 
 ts_project(
     name = "file_system_fake",
-    srcs = ["file_system_fake.ts"],
+    srcs = ["file_system_fake.mts"],
     visibility = ["//visibility:public"],
     testonly = True,
     deps = [
@@ -88,14 +88,14 @@ ts_project(
 
 ts_project(
     name = "http",
-    srcs = ["http.ts"],
+    srcs = ["http.mts"],
     visibility = ["//visibility:public"],
     deps = ["//:node_modules/@types/node"],
 )
 
 ts_project(
     name = "http_test_lib",
-    srcs = ["http_test.ts"],
+    srcs = ["http_test.mts"],
     testonly = True,
     deps = [
         ":http",
@@ -139,7 +139,7 @@ paths_test_suite(name = "paths_test")
 
 ts_project(
     name = "prerender_annotation_walker",
-    srcs = ["prerender_annotation_walker.ts"],
+    srcs = ["prerender_annotation_walker.mts"],
     visibility = ["//visibility:public"],
     deps = [
         "//common/models:prerender_annotation",
@@ -149,7 +149,7 @@ ts_project(
 
 ts_project(
     name = "prerender_annotation_walker_test_lib",
-    srcs = ["prerender_annotation_walker_test.ts"],
+    srcs = ["prerender_annotation_walker_test.mts"],
     testonly = True,
     data = ["//:node_modules/node-html-parser"],
     deps = [
@@ -167,13 +167,13 @@ jasmine_node_test(
 
 ts_project(
     name = "probably",
-    srcs = ["probably.ts"],
+    srcs = ["probably.mts"],
     visibility = ["//visibility:public"],
 )
 
 ts_project(
     name = "probably_test_lib",
-    srcs = ["probably_test.ts"],
+    srcs = ["probably_test.mts"],
     testonly = True,
     deps = [
         ":probably",

common/binary_test.ts → common/binary_test.mts

@@ -1,4 +1,4 @@
-import { main as mainReal } from './binary';
+import { main as mainReal } from './binary.mjs';
 
 // Wrap `main`'s type to return its `Promise` to easily `await` it.
 function main(...args: Parameters<typeof mainReal>): Promise<void> {

common/collections_test.ts → common/collections_test.mts

@@ -1,4 +1,4 @@
-import { unique } from './collections';
+import { unique } from './collections.mjs';
 
 describe('collections', () => {
     describe('unique()', () => {

common/file_system_fake.ts → common/file_system_fake.mts

@@ -1,5 +1,5 @@
 import * as path from 'path';
-import { FileSystem } from './file_system';
+import { FileSystem } from './file_system.mjs';
 
 /**
  * A fake implementation of the `FileSystem` interface which stores everything

common/formatters_test.ts → common/formatters_test.mts

@@ -1,4 +1,4 @@
-import { mdSpacing } from './formatters';
+import { mdSpacing } from './formatters.mjs';
 
 describe('formatters', () => {
     describe('spaceMarkdown()', () => {

common/http_test.ts → common/http_test.mts

@@ -1,6 +1,6 @@
 import nodeHttp from 'http';
 import { URL } from 'url';
-import * as http from './http';
+import * as http from './http.mjs';
 
 describe('http', () => {
     describe('get', () => {

common/models/BUILD.bazel

@@ -3,13 +3,13 @@ load("//tools/typescript:defs.bzl", "ts_project")
 
 ts_project(
     name = "prerender_annotation",
-    srcs = ["prerender_annotation.ts"],
+    srcs = ["prerender_annotation.mts"],
     visibility = ["//visibility:public"],
 )
 
 ts_project(
     name = "prerender_annotation_test_lib",
-    srcs = ["prerender_annotation_test.ts"],
+    srcs = ["prerender_annotation_test.mts"],
     testonly = True,
     deps = [
         ":prerender_annotation",
@@ -24,21 +24,21 @@ jasmine_node_test(
 
 ts_project(
     name = "prerender_annotation_mock",
-    srcs = ["prerender_annotation_mock.ts"],
+    srcs = ["prerender_annotation_mock.mts"],
     testonly = True,
     visibility = ["//visibility:public"],
     deps = [":prerender_annotation"],
 )
 
 ts_project(
     name = "prerender_metadata",
-    srcs = ["prerender_metadata.ts"],
+    srcs = ["prerender_metadata.mts"],
     visibility = ["//visibility:public"],
 )
 
 ts_project(
     name = "prerender_metadata_test_lib",
-    srcs = ["prerender_metadata_test.ts"],
+    srcs = ["prerender_metadata_test.mts"],
     testonly = True,
     deps = [
         ":prerender_metadata",
@@ -53,22 +53,22 @@ jasmine_node_test(
 
 ts_project(
     name = "prerender_metadata_mock",
-    srcs = ["prerender_metadata_mock.ts"],
+    srcs = ["prerender_metadata_mock.mts"],
     testonly = True,
     visibility = ["//visibility:public"],
     deps = [":prerender_metadata"],
 )
 
 ts_project(
     name = "prerender_resource",
-    srcs = ["prerender_resource.ts"],
+    srcs = ["prerender_resource.mts"],
     visibility = ["//visibility:public"],
     deps = [":url_path"],
 )
 
 ts_project(
     name = "prerender_resource_test_lib",
-    srcs = ["prerender_resource_test.ts"],
+    srcs = ["prerender_resource_test.mts"],
     testonly = True,
     deps = [
         ":prerender_resource",
@@ -83,12 +83,12 @@ jasmine_node_test(
 
 ts_project(
     name = "url_path",
-    srcs = ["url_path.ts"],
+    srcs = ["url_path.mts"],
 )
 
 ts_project(
     name = "url_path_test_lib",
-    srcs = ["url_path_test.ts"],
+    srcs = ["url_path_test.mts"],
     testonly = True,
     deps = [
         ":url_path",

common/models/prerender_annotation_mock.ts → common/models/prerender_annotation_mock.mts

@@ -3,7 +3,7 @@
  * @see /README.md#Mocking
  */
 
-import { PrerenderAnnotation, ScriptAnnotation, StyleAnnotation } from './prerender_annotation';
+import { PrerenderAnnotation, ScriptAnnotation, StyleAnnotation } from './prerender_annotation.mjs';
 
 /**
  * Mocks a {@link PrerenderAnnotation} object. Since this type is a

common/models/prerender_annotation_test.ts → common/models/prerender_annotation_test.mts

@@ -1,4 +1,4 @@
-import { PrerenderAnnotation, createAnnotation, parseAnnotation, ScriptAnnotation, annotationsEqual, StyleAnnotation } from './prerender_annotation';
+import { PrerenderAnnotation, createAnnotation, parseAnnotation, ScriptAnnotation, annotationsEqual, StyleAnnotation } from './prerender_annotation.mjs';
 
 describe('prerender_annotation', () => {
     describe('PrerenderAnnotation', () => {

common/models/prerender_metadata_mock.ts → common/models/prerender_metadata_mock.mts

@@ -3,7 +3,7 @@
  * @see /README.md#Mocking
  */
 
-import { PrerenderMetadata, ScriptMetadata } from './prerender_metadata';
+import { PrerenderMetadata, ScriptMetadata } from './prerender_metadata.mjs';
 
 /** Mocks the {@link PrerenderMetadata} object with the given overrides. */
 export function mockPrerenderMetadata(

common/models/prerender_metadata_test.ts → common/models/prerender_metadata_test.mts

@@ -1,4 +1,4 @@
-import { PrerenderMetadata, ScriptMetadata } from './prerender_metadata';
+import { PrerenderMetadata, ScriptMetadata } from './prerender_metadata.mjs';
 
 describe('prerender_metadata', () => {
     describe('PrerenderMetadata', () => {

common/models/prerender_resource.ts → common/models/prerender_resource.mts

@@ -1,4 +1,4 @@
-import { UrlPath } from './url_path';
+import { UrlPath } from './url_path.mjs';
 
 /** Represents a resource to be rendered / generated at a particular path. */
 export class PrerenderResource {

common/models/prerender_resource_test.ts → common/models/prerender_resource_test.mts

@@ -1,4 +1,4 @@
-import { PrerenderResource } from './prerender_resource';
+import { PrerenderResource } from './prerender_resource.mjs';
 
 describe('PrerenderResource', () => {
     describe('of()', () => {

common/models/url_path_test.ts → common/models/url_path_test.mts

@@ -1,4 +1,4 @@
-import { UrlPath } from './url_path';
+import { UrlPath } from './url_path.mjs';
 
 describe('UrlPath', () => {
     describe('of()', () => {

common/prerender_annotation_walker.ts → common/prerender_annotation_walker.mts

@@ -1,5 +1,5 @@
 import { CommentNode, HTMLElement, Node } from 'node-html-parser';
-import { parseAnnotation, PrerenderAnnotation } from './models/prerender_annotation';
+import { parseAnnotation, PrerenderAnnotation } from './models/prerender_annotation.mjs';
 
 /**
  * A reference to a `node-html-parser` `Node` which contains a
@@ -138,4 +138,4 @@ function* walk(node: Node, parent?: HTMLElement):
             yield* walk(child, node);
         }
     }
-}
+}

common/prerender_annotation_walker_test.ts → common/prerender_annotation_walker_test.mts

@@ -1,6 +1,6 @@
 import { HTMLElement, parse } from 'node-html-parser';
-import { createAnnotation } from './models/prerender_annotation';
-import { walkAllAnnotations } from './prerender_annotation_walker';
+import { createAnnotation } from './models/prerender_annotation.mjs';
+import { walkAllAnnotations } from './prerender_annotation_walker.mjs';
 
 describe('prerender_annotation_walker', () => {
     describe('walkAllAnnotations()', () => {

common/probably_test.ts → common/probably_test.mts

@@ -1,4 +1,4 @@
-import { definitely, Definitely, Probably } from './probably';
+import { definitely, Definitely, Probably } from './probably.mjs';
 
 interface User {
     name: string;