Update task orgs with existing tasks

- Move stack task org calls up to task
- If the task organizer dies, reset the last cached wm mode and update
  all existing tasks when the task organizer is next re-registered. This
  only applies to the first task organizer for a given windowing mode
  to ensure that the testing strategy of only reporting new tasks to
  current task organizers still applies.

Bug: 150874492
Test: atest WmTests:TaskOrganizerTests
Test: Move pip, kill sysui, ensure sysui still controls pip task
Change-Id: Ib266f67243ea215940747d57022d3aa91d55dff8