fix(compiler): walk third party modules (#12453)

fixes #11889
fixes #12428

modules/@angular/compiler-cli/integrationtest/third_party_src/comp.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
+ */
+
+import {Component} from '@angular/core';
+
+@Component({
+  selector: 'third-party-comp',
+  template: '<div>3rdP-component</div>',
+})
+export class ThirdPartyComponent {
+}