eefer dispatching recents transition changes

When the recents transition happen, defer dispatch of tasks that are
going to be hidden until we know the end state of them.

Bug: 400787468
Test: atest DesktopTaskChangeListenerTest
Test: atest FreeformTasksTransitionObserverTest
Flag: com.android.window.flags.enable_windowing_transition_handlers_observers
Change-Id: Ib32c92a014e48449b78642a27d6aa9452977ec5f