Move correct stack to front when split-screen is dismissed

- In AMS.dismissSplitScreenMode move the split-screen secondary stack to
the front if the split-screen primary stack shouldn't be focused after
it goes fullscreen.
- In AD.onSplitScreenModeDismissed the the top-most fullscreen stack
regardless of windowing mode to determine if home stack should be moved.
We also want this movement for things like the recents activity.

Test: Manual steps from bug
Change-Id: If07abcd0d0d50c846bb282e65968c883717c6462
Fixes: 72044176