test(integration): add an env for testing closure builds (#14130)

* feat: add an env for testing closure builds
* build(npm): add dev dependency on yarn (and remove dev props for readability)
* build: refactor integration test runner

integration/hello_world__closure/src/hello-world.component.ts

@@ -0,0 +1,10 @@
+import {Component, Injectable} from '@angular/core';
+
+@Component({
+  selector: 'hello-world-app',
+  template: '<div>Hello {{ name }}!</div>',
+})
+@Injectable()
+export class HelloWorldComponent {
+  name: string = 'world';
+}