Add "Manage Windows" option to Handle Menu.

When 2 or more app instances are open, handle menu will show a "Manage
Windows" button. This button will open a sub menu showing thumbnails of
all open instances of the app that aren't the same instance that
opened the menu.

Clicking a thumbnail closes the menu and opens the instance, following
similar rules to the Add Window button:

-In freeform, open the instance as a new freeform window (or move it
to the front if already in freeform).
-In fullscreen, open the instance in splitscreen.
-In splitscreen, replace the opposite split stage with the requested
instance.

Still to do:
- Thumbnails of freeform tasks do not use the snapshot cache.
- Animation of menu
- Polish of menu and icons
- Max height/scrollability for menus with > 6 instances.

Video: http://recall/-/g32sLZz1OjS8b4rbGPPq6V/g7RFA4hRn5LFHUcc4Dvpqx
Bug: 336289597
Bug: 337903443
Flag: com.android.window.flags.enable_desktop_windowing_multi_instance_features
Test: manual
Change-Id: I0e8880a35c210df6ec272c23eb7c685e47174a09