[PIP2] Fix stashed state updates.

Recall: http://recall/clips/dac41c2f-66cd-4558-a310-71f81f8819d1

Unstashing PiP via tapping was not working due to PiP stashed state not
being updated correctly, since the stashed state was being checked in
stashEndActionIfNeeded before the PiP bounds was updated internally.
This CL updates the logic flow so the stashed status is only checked and
updated after the PiP bounds are updated.

Bug: 374165615
Test: Launch PiP and verify stashing/unstashing works as expected
Flag: com.android.wm.shell.enable_pip2
Change-Id: I3d0787164a98bcabcfe79425b5b6b13eb62e65ba