[PiP on Desktop] Fix multi-activity PiP switching in and out of Desktop

When switching in and out of Desktop session, multi-activity PiP
expanding is misbehaving. This CL adds the following changes:
- If PiP is entered while in Desktop then expanded in fullscreen, the
  wct needs to be updated with addMoveToFullscreenChanges so that
Desktop cleanup and changes is performed
- If PiP is entered while in fullscreen then expanded in Desktop, the
  parent needs to be moved to the Desk. If no Desk is active, Desk
activation changes need to be added as well (only applicable for empty
desks scenario).

Bug: 423087090
Test: atest DesktopPipTransitionControllerTest
Test: atest WMShellUnitTests:com.android.wm.shell.pip2
Test: atest WMShellUnitTests:com.android.wm.shell.common.pip
Test: Manual - enter multi-activity PiP from fullscreen, enter Desktop
session then expand PiP. Verify PiP expands to Desktop task and Desktop
is WAI. Enter PiP via minimize, exit Desktop session then expand PiP.
Verify PiP expands to fullscreen.
Flag: com.android.window.flags.enable_desktop_windowing_pip

Change-Id: I9436e2dfd156cd440d93f8077a9b540047bb466a