build(docs-infra): update project structure to cli@9 10/12 (tsconfig.json) (#36015)

Update `tsconfig[.*].json`.
Also, all make necessary changes to ensure the example apps can be
successfully built with the new, stricter type-checking options.

PR Close #36015

aio/content/examples/elements/src/app/popup.component.ts

@@ -39,7 +39,7 @@ import { animate, state, style, transition, trigger } from '@angular/animations'
   `]
 })
 export class PopupComponent {
-  private state: 'opened' | 'closed' = 'closed';
+  state: 'opened' | 'closed' = 'closed';
 
   @Input()
   set message(message: string) {