build(docs-infra): update AIO to align with new v13.0.0-next.9 CLI apps (#43686)

This commit updates angular.io to more closely align with new apps
created with the latest Angular CLI and remove redundant files/config
now that CLI has dropped support for differential loading.

PR Close #43686

aio/src/testing/doc-viewer-utils.ts

@@ -17,17 +17,19 @@ import { ElementsLoader } from 'app/custom-elements/elements-loader';
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
 export class TestDocViewerComponent extends DocViewerComponent {
-  currViewContainer: HTMLElement;
-  nextViewContainer: HTMLElement;
+  override currViewContainer: HTMLElement;
+  override nextViewContainer: HTMLElement;
 
   // Only used for type-casting; the actual implementation is irrelevant.
-  prepareTitleAndToc(_targetElem: HTMLElement, _docId: string): () => void { return null as any; }
+  override prepareTitleAndToc(_targetElem: HTMLElement, _docId: string): () => void {
+    return null as any;
+  }
 
   // Only used for type-casting; the actual implementation is irrelevant.
-  render(_doc: DocumentContents): Observable<void> { return null as any; }
+  override render(_doc: DocumentContents): Observable<void> { return null as any; }
 
   // Only used for type-casting; the actual implementation is irrelevant.
-  swapViews(_onInsertedCb?: () => void): Observable<void> { return null as any; }
+  override swapViews(_onInsertedCb?: () => void): Observable<void> { return null as any; }
 }