Only handle resize touches if starting gesture within resize area

- Only dispatch touch events to the resize gesture handler if started
  within the touch area (and reset the touch state to prevent normal
  handling)
- Fix an issue with being able to drag on the pip edge touching the edge
  of the screen due to the movement bounds not taking the resized pip
  into account

Bug: 160160987
Test: Repeatedly swipe on the drag handle on the edge of the screen

Change-Id: Id616c7ee2ee102f26de83e827589058ff24987ef