Ensure applying saved fraction when re-entering PiP

1. Resets PiP fraction once the app is stopped

When in gesture navigation mode, setHidden can be called ahead of
enterPictureInPictureMode, which results the fraction being reset before
accessing the last saved value.

2. Do not set mBoundsAnimating* variables for FADE_IN animation

Bug: 135224920
Test: Manually enter and exit PiP mode
Change-Id: I93d77071d72a2695e510372dff3a48bf97209b8d