Defer window removal including app transition

The mWinAnimator.applyAnimationLocked in removeIfPossible may
not apply window level animation, but the activity may be
running closing transition. So the window shouldn't be removed
immediately, otherwise the animation is disappeared.

Bug: 176471456
Test: WindowStateTests#testDeferredRemovalByAnimating
Test: Launch a translucent activity and finish it, check the
      slide-down style exit animation can play with the
      declared duration.

Change-Id: I4227a89108d16fc25f912b96ae83cf125fec4b16