fix(builtin): look in the execroot for nodejs_binary source entry_points

In a6e29c2 we added support for generated entry_point by adding a secondary lookup.
In 863c7de we reversed the order of the lookups to make rollup work in a certain use case.
Neither of these was principled, because we know ahead of time whether the entry_point is generated. We can use a single lookup.

This also makes sure that programs run in the location where the linker will put them (note that the logic in question runs before the linker has created the node_modules directory in the execroot.)
This is why bazel-contrib#1787 observes that some node programs were broken - we were running the entry point as
bazel-out/host/bin/external/npm/@graphql-codegen/cli/bin/graphql-codegen.sh.runfiles/npm/node_modules/@graphql-codegen/cli/bin.js
when it should have been
node_modules/@graphql-codegen/cli/bin.js

Fixes bazel-contrib#1787

internal/node/launcher.sh

@@ -191,10 +191,7 @@ for ARG in "${ALL_ARGS[@]:-}"; do
   case "$ARG" in
     --bazel_node_modules_manifest=*) MODULES_MANIFEST="${ARG#--bazel_node_modules_manifest=}" ;;
     --nobazel_patch_module_resolver)
-      declare MAIN="TEMPLATED_entry_point_execroot_path"
-      if [[ ! -f "$MAIN" ]]; then
-        MAIN=$(rlocation "TEMPLATED_entry_point_manifest_path")
-      fi
+      MAIN="TEMPLATED_script_path"
       LAUNCHER_NODE_OPTIONS=( "--require" "$node_patches_script" )
 
       # In this case we should always run the linker

internal/node/node.bzl

@@ -246,8 +246,6 @@ fi
         #       Need a smarter split operation than `expanded_arg.split(" ")` as it will split
         #       up args with intentional spaces and it will fail for expanded files with spaces.
         "TEMPLATED_args": " ".join(expanded_args),
-        "TEMPLATED_entry_point_execroot_path": _to_execroot_path(ctx, ctx.file.entry_point),
-        "TEMPLATED_entry_point_manifest_path": _to_manifest_path(ctx, ctx.file.entry_point),
         "TEMPLATED_env_vars": env_vars,
         "TEMPLATED_expected_exit_code": str(expected_exit_code),
         "TEMPLATED_link_modules_script": _to_manifest_path(ctx, ctx.file._link_modules_script),
@@ -259,6 +257,12 @@ fi
         "TEMPLATED_runfiles_helper_script": _to_manifest_path(ctx, ctx.file._runfiles_helper_script),
         "TEMPLATED_vendored_node": "" if is_builtin else strip_external(ctx.file._node.path),
     }
+
+    if ctx.file.entry_point.is_source:
+        substitutions["TEMPLATED_script_path"] = _to_execroot_path(ctx, ctx.file.entry_point)
+    else:
+        substitutions["TEMPLATED_script_path"] = _to_manifest_path(ctx, ctx.file.entry_point)
+
     ctx.actions.expand_template(
         template = ctx.file._launcher_template,
         output = ctx.outputs.launcher_sh,