Attach PipSnapshotContentOverlay in PipTransition

Similar to what's in PipTaskOrganizer, we try to apply the snapshot
overlay when entering PiP, which was missing in PipTransition with
shell-transition being on.

Video: http://recall/-/aaaaaabFQoRHlzixHdtY/cII9Y55L2gdPRhhweur6KT
Bug: 283822454
Test: manual, see Video
Change-Id: I9041a808f0842e005659f59327a56802a02168a4