Add transition when swiping from fullscreen to enter PiP

There are some artifacts actually come from test app implementation
- when in landscape fullscreen, sourceRectHint would include the black
  background on both sides
- when settled in PiP, app does the transition which causes the final
  glitch
Would address these later in the test app itself

Video: http://rcll/aaaaaabFQoRHlzixHdtY/cOco1yoMXwFzSifFqQET9U
Video: http://rcll/aaaaaabFQoRHlzixHdtY/f3IWG09DRO9aUNnzqSdPLU
Bug: 171802909
Test: see video
Change-Id: I783e51e78277b1179a7e8de50050b7c9e1a6de17