[RESTRICT AUTOMERGE] Remove staled pinned Task upon SystemUI reboot

Added a timeout callback in PipTaskOrganizer#onTaskAppeared, remove the
staled pinned task if there is no transition state change follows.

Flag: EXEMPT bugfix
Bug: 376048041
Test: Run the PoC app and make sure no background Activity launch
Test: atest PinnedStackTests
Change-Id: Ic9d1203cc72240f2fdcd5df3f2cab8e5af8e4a4b