fix(magnification): magnification should not reset when pressing on navigation bar

As b/324949652, the AccessibilityController#onWMTransition callback would be triggered when the finger down event on navigation bar to bring the recents window to front, then the controller would notify the magnification about the context changed and cause the magnification being reset. Then the following gesture events to trigger the acccessibility shortcut will activate the magnification again.

Therefore, if the onWMTransition callback is triggered with RECENT flag, we'll delay the notifying of the context changed, then send it if there is a following onFocusChanged callback triggered. That's because if there is a delayed notification for recents to front transition and onFocusChanged is triggered, we assume that the users leave current window to the home/recents window, thus we'll need to send the delayed notification. Before the onFocusChanged, if there are some other transitions causing the notifying, or the recents/home window is removed, then we won't need the delayed notification anymore.

Bug: 324949652
flag: ACONFIG com.android.window.flags.delay_notification_to_magnification_when_recents_window_to_front_transition DEVELOPEMENT
Test: manually flipping the flag
      atest cts/FullScreenMagnificationGestureHandlerTest
Change-Id: I0183edda87e7278bcf69f4fe7e156854cc80bf89