refactor(compiler): store metadata of top level symbols also in summaries (#13289)

This allows a build using summaries to not need .metadata.json files at all
any more.

Part of #12787

modules/@angular/compiler/src/injectable.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
+ */
+
+/**
+ * A replacement for @Injectable to be used in the compiler, so that
+ * we don't try to evaluate the metadata in the compiler during AoT.
+ * This decorator is enough to make the compiler work with the ReflectiveInjector though.
+ */
+export function CompilerInjectable(): (data: any) => any {
+  return (x) => x;
+}