Defer display switch update if transition is running

WindowManager receives updates from DisplayManager through
onDisplayChanged() callback by reading the DisplayInfo
objects after receiving this callback.  This CL makes
WindowManager to defer the updates if there is a collecting
Shell transition. This is needed to allow starting physical
display change transition if there is another transition
running.

Previously this was silently failing without starting
a display switch transition.  It also changes the behavior
of PhysicalDisplayTransitionLauncher: now it starts the
display change transition even if it's not an 'unfold' transition.
UnfoldTransitionHandler will decide if it wants to handle
'unfold' display change and default transition handler will be used otherwise.

Bug: 259220649
Bug: 277866717
Test: atest PhysicalDisplaySwitchTransitionLauncherTest
Test: atest DisplayContentTests
Test: manual fold/unfold with apps/split screen/
  split screen + PIP
Change-Id: Ib0d0624bf141ff16578d7902bec98272d17ee36f