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

Closes #14509

modules/@angular/router/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 router package.
- */
-export * from './src/index';
+// 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';