Allow children task of created-by-organizer task to be organized

Allows to organize direct child of root task created by organizer and
extends TaskInfo to reveal the parent task id.

To organize child task properly for each features, passes all child
task organizer events to the listener listening to its parent task if
feasible.

Fix: 169267298
Fix: 169266482
Test: atest WindowOrganizerTests
Test: atest SplitScreenTests
Test: atest PinnedStackTests
Test: atest WindowInsetPolicyTests
Test: atest WMShellUnitTests
Test: split screen works
Change-Id: I8e66f810c86fcdac3287adfa208d8e34786fc9b5