Opt-in desktop mode's drag PendingIntent for BAL

Otherwise the transient launch of Home is not executed which prevents
the drag-to-desktop transition from being usable.

Also adds handling of aborted transitions to recover to a usable state
instead of crashing the system.

Bug: 312507707
Bug: 301106941
Test: atest DragToDesktopTransitionHandlerTest
Test: manual - drag from fullscreen, see animation and transition work
Change-Id: I59799510350d89556a83f108a12dd3485bffade6