PiP: update magnetic field radius for dismissmal as PiP resizes.

As PiP gets bigger, it should be that user doesn't have to put their
fingers as close as before to the dismiss bubble before it magnetizes
and pulls in PiP.

Bug: 164947242
Test: Manual. Resize PiP to larger and try to drag to dismiss bubble.
Change-Id: I2ec0fbfd87bc010d9ca551df0eeb77a22c02c6dc