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

Closes #14509

modules/@angular/common/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 common package.
+ */
+export * from './src/common';
+
+// This file only reexports content of the `src` folder. Keep it that way.