Fix SplitContainer not updated when folded.

The root cause is that TaskFragmentParentInfo wasn't be dispatched
when there's a display or visibility change because we didn't
implement getTaskFragment() in TaskFragment and it led to
the TskFragment can't return itself if the predicate function
returns true.

This CL fixes WC#getTaskFragment and changes to dispatch
Task#shouldBeVisible instead of Task#isVisibleRequested.
The reason is that the visibleRequested change is not early enough for
the scenario that device is folded from unfolded state, and lead to
Settings flickering.

Test: manual - open Settings and fold the device
Test: atest TaskTests#testGetTaskFragment
Test: atest TaskFragmentOrganizerControllerTest ActivityRecordTests
fixes: 249055633
Change-Id: Ie1c56758697d14b426c9ed713da84e49c9f880d8