Fix split cannot active if app trampoline launch new task

This reverts commit 2a47e6a6 and
commit 76ab53a3.

Both CL cause regression which lead to users cannot active split
by some apps use trampoline launch new task on launcher icon. So
fix it by revert both CLs.

Other changes are also for fixing this case. There is a timing
issue and we cannot ensure the old trampoline still remain under
split root when we get remote animation callback. Fix it by only
checking any children tasks are under split root or not.

Bug: 278172065
Test: manual
Test: pass existing tests
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:6e29d4ddb8ab2cb9b66539c0b9bc3e15efe8b885)
Merged-In: Ibd6d9a8377e4b5327a473f8b9adf4e569e826172
Change-Id: Ibd6d9a8377e4b5327a473f8b9adf4e569e826172