Start a new transition to ignore split-enter from a malformed transition

- If two tasks are started in immediately one after the other in order
  with the latter being an adjacent launch, the launch of the two tasks
  can end up in the same transition but the transition request will
  report the first task launch as the trigger task. As a result,
  StageCoordinator will not be resolved as the handler for the
  transition and the enter transition not play correctly (falling
  through the default transition handler which only shows the adjacent
  task without being in split).

  If we detect this rare edge case, we instead restore the adjacent task
  to the TaskDisplayArea instead of treating it as an adjacent launch.

Bug: 405392600
Flag: EXEMPT bugfix
Test: atest SplitTransitionUtilsTests
Test: Manual, with test app from b/405392600
(cherry picked from commit 3be8f7ff61baa3a98320de393a94735aecc6e77c)
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:6d8942c121f60a82e7de9ba83d81b860b713b541
Merged-In: I88f43913431c5be8ca736c1bd074804a2c9f61fe
Change-Id: I88f43913431c5be8ca736c1bd074804a2c9f61fe