message: docs(upgrade): add `@extensible` to the `UpgradeComponent` class
  This class is designed to be used as a base class. Therefore it should not be
  marked as `final` in the API docs.
  PR Close
diff: @@ -65,6 +65,7 @@ class Bindings {
  * * the `ElementRef` and `Injector` for the component wrapper
  *
  * @publicApi
  + * @extensible
  */
  @Directive()
  export class UpgradeComponent implements OnInit, OnChanges, DoCheck, OnDestroy {
  