Merge changes I619be025,I126765a3,I0307c191,I9425785f,I623bd48d, ...

* changes:
  Restore changes lost during merge
  Fix flicker at the end of docked stack divider animation
  Implement divider UX interactions
  Immediately start resizing when touching docked divider
  Fix black holes and flickering in docked resizing
  Migrate docked divider drawing to SysUI
  Supply app transition specs with a future