Use transient Home launch in enter/cancel transition

Replaces the existing enter and cancel desktop transitions from a drag
of the caption handle with a new implementation that uses a transient
launch of Home to defer WC changes (e.g. windowing mode / bounds)
until the user "commits" to entering desktop by releasing the drag.
If the gesture is cancelled, then the CANCEL transition restores the
pre-drag order.
Also handles drag to desktop from split screen differently: cancelling
means that the task goes back into its original split position whereas
before it cancelled into fullscreen.

Bug: 301106941
Test: atest DragToDesktopTransitionHandlerTest
Test: manual - drag fullscreen task to desktop, no flickers and
end state is fine (both from fullscreen and split screen)

Change-Id: I41221eeb99013da35e83d7d3760dbec5e5e3fa62