Fix issues with incorrectly handling transitions as bubble transitions

- Change to looking up app bubbles by task id as
  getAppBubbleKeyForTask() may generate the same key as bubble keys.
  This was causing issues where we should have been falling into
  TaskViewTransitions to switch between existing bubbles, but was
  incorrectly identifying the existing bubble
- For the same reason, we should also ignore intercepting bubble task
  launch transitions for existing bubbled tasks entirely (just let it
  fall through when existing). This can happen for cases where a
  bubbled task launches a new task for an app that is already bubbled

Bug: 411271022
Flag: com.android.wm.shell.enable_create_any_bubble
Test: atest DefaultMixedHandlerTest
Test: Open various trampoline apps into a bubble
Change-Id: I23fad15eba3f4213972cd9f7b752e204b2b34167