Freezing screen when dismiss pip if orientation is going to change.

When skip pip animation to fullscreen, the stack will move to another
fullscreen stack then resume top activity, if one of activity is not
paused, the remaining resume steps will be skip till all activities
paused. In that case the fullscreen stack will shows up before rotation
animation.
To let the animation smooth, freeze screen once we know the orientation
is going to change when dismiss pip.

Fix: 138820136
Test: atest ActivityLifecyclePipTests
Change-Id: I808b1a797a322ffce039de4bcad316973e732672