Implement auto-enter PiP2 in gesture nav [5/N]

Handle the case where the app provided source-rect-hint
is either invalid or null.

Make sure the overlay originally created in Launcher
is reparented properly, manipulated to look invariant
despite deferred resetSurfaceTransform() in
Transition#commitConfigAtEndActivities().
For this we use setBoundsChangeTransaction().

On the Core side, a newly created SyncGroup sets up our WindowState with
a non-zero mPrepareSyncSeqId to make sure that
draw handler modified transactions are merged into
the transaction altered by resetSurfaceTransform() later.

Bug: 325481148
Test: manually swipe-up to enter PiP with an invalid srcRectHint
Change-Id: I3f0853a0f06576a90914e6a200039fdb826deafb