build(bazel): Turning on strictPropertyInitialization for Angular. (#24572)

All errors for existing fields have been detected and suppressed with a
`!` assertion.

Issue/24571 is tracking proper clean up of those instances.

One-line change required in ivy/compilation.ts, because it appears that
the new syntax causes tsickle emitted node to no longer track their
original sourceFiles.

PR Close #24572

packages/common/src/directives/ng_plural.ts

@@ -46,8 +46,10 @@ import {SwitchView} from './ng_switch';
  */
 @Directive({selector: '[ngPlural]'})
 export class NgPlural {
-  private _switchValue: number;
-  private _activeView: SwitchView;
+  // TODO(issue/24571): remove '!'.
+  private _switchValue !: number;
+  // TODO(issue/24571): remove '!'.
+  private _activeView !: SwitchView;
   private _caseViews: {[k: string]: SwitchView} = {};
 
   constructor(private _localization: NgLocalization) {}