Clean up split after trampolines

- If a task trampoline gets collected into the same transition but after
  the transition request is handled, then StageCoordinator does not have
  an opportunity to detect and clean up after the change.  Instead, we
  try to detect that case and clean up split so it is not left in an
  inconsistent state

Bug: 426116216
Flag: EXEMPT bugfix
Test: Split trampoline app with another app, go home and relaunch
      trampoline app
Change-Id: Ifaa91f6b7f49b1e02d7b3c4ff68e7a7d7f07ff2f