build: produce metadata bundles for @angular modules (#14509)

Closes #14509

modules/@angular/forms/index.ts

@@ -6,11 +6,9 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-/**
- * @module
- * @description
- * Entry point for all public APIs of the forms package.
- */
-export * from './src/forms';
+// This file is not used to build this module. It is only used during editing
+// by the TypeScript language serivce and during build for verifcation. `ngc`
+// replaces this file with production index.ts when it rewrites private symbol
+// names.
 
-// This file only reexports content of the `src` folder. Keep it that way.
+export * from './public_api';

modules/@angular/forms/public_api.ts

@@ -0,0 +1,16 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+/**
+ * @module
+ * @description
+ * Entry point for all public APIs of the forms package.
+ */
+export * from './src/forms';
+
+// This file only reexports content of the `src` folder. Keep it that way.

modules/@angular/forms/tsconfig-build.json

@@ -25,11 +25,13 @@
     "types": []
   },
   "files": [
-    "index.ts",
+    "public_api.ts",
     "../../../node_modules/zone.js/dist/zone.js.d.ts"
   ],
   "angularCompilerOptions": {
     "annotateForClosureCompiler": true,
-    "strictMetadataEmit": true
+    "strictMetadataEmit": true,
+    "bundleIndex": "index",
+    "importAs": "@angular/forms"
   }
 }