Reduce jank during pinned stack animation

- Don’t launch Pip overlay activities during pinned stack animation.
This causes extra CPU load and takes a way resources from the running
animation.
- Finish Pip overlay activities before starting pinned stack resize
animation. Reduces the amount of work the system needs to do to keep
the overlays in-sync with the other activities in the pinned stack.
- Use AM.resizeStack with null bounds to take Pip to fullscreen so that
we can animate the bounds changed.
- Also, fixed Activity.enterPictureInPicture API to animate the transition
if Pip is entered from the app instead of Pip manager.

Bug: 25672053
Change-Id: I82399c10f1b8c675ea3861ba973dc8ecfbfbe50f