Fix a few issues with the recents transition

- Preempt the bookeend transition if one has already been sent and a
  new (unexpected) transition is merged ahead of it, at that point
  core has already changed as a part of the incoming transition so
  restoring the transient order may not result in any changes
- Only use the bookend transition when there are changes that affect
  the window hierarchy or other transitions, otherwise, continue
  using finishWCT for now if we are just updating unrelated container
  properties
- Add some logs when silently skipping pausing due to a transient
  launch resumed activity
- Add some docs on transient transitions

Bug: 346588978
Flag: EXEMPT com.android.wm.shell.enable_recents_bookend_transition
Test: atest NexusLauncherTests:TaplStartLauncherViaGestureTests#testStressSwipeToOverview
Test: atest RecentsTransitionHandlerTest

Change-Id: Id1b05ab56976d332518eb71e099d1993211c474e
Signed-off-by: Winson Chung <winsonc@google.com>