Fix issue with lagging pip movement after entering/exiting dismiss

- Increase the spring stiffness to catch up to the finger sooner
- In certain cases, moving into and out of the dismiss area quickly
  will start the physics animator multiple times which can trigger
  the update callback multiple times per frame, so only update if
  the bounds have changed

Bug: 183756396
Test: Drag into and out of the
Change-Id: I85a94948ef23b9dc1d569ab3706af899e0d67ef1