Disallow concurrent recents transitions for the same display

- Launcher only handles a single recents transition at a time, and
  multiple running transitions can cause problems since the second
  will attempt to merge into the first started transition.
- Also tweak some protologs so they are easier to search for in the
  code

Bug: 432103567
Flag: EXEMPT bugfix
Test: atest RecentsTransitionHandlerTest
Change-Id: Ie7895fe77cb50e7703d0105cef9a18dc1156993f