[Shell-Transition] clean-up some isAnimating call points

..to reflect the app transition animating state when shell-transition
enabled for below cases:

1) ImeInsetsSourceProvider#isReadyToShowIme will use WS#isClosing ->
   AR#isClosingOrEnteringPip to check if the IME layering target window
   is in closing transition. (i.e. It won't be ready to show IME while
   the target is in closing app transition.) Also, given isClosing and
   isClosingOrEnteringPip currently is only used for checking IME target
   validity, wraping those logic into isImeTargetWindowClosing() for
   simplicity.

2) With Shell-Transition, the activity will running a transition when
   it is visible, it won't be included when fromTransition is true means
   the call from finishTransition. As a result, in AR#commitVisibility,
   callback onAppVisibilityChanged(visible, runningAppAnimation) with
   using the above checking logic and adding logs for tracking. In case
   a11y controller will always callback onWindowTransition with
   TRANSIT_EXIT due to runningAppAnimation always being false by
   isAnimating no-op.

Fix: 212570341
Test: No visible change & Pass existing tests.
Change-Id: I9cc77956b3ff61ae83f5bd120c395cc6aca93af9