[PiP2] Implement expand in fixed rotation

Implement exit-via-expand with fixed rotation
in PiP2.

Also modified WindowToken#getOrCreateFixedRotationLeash()
to not have a fixed rotation leash created when dealing
with a PiP activity (we check for win-mode at transition start,
since we reparent and set windowing mode right away in PiP2).
This should make sure that Shell receives the activity leash,
and that we have no fixed rotation transforms applied on it
during the expand animation.

Bug: 376302431
Flag: com.android.wm.shell.enable_pip2
Test: enter single-activity PiP, then expand
Change-Id: Id6d592876fdd6581ed5a111f0e64d10222296016