Add ability to fling to dismiss PIP from anywhere

This is by default turned off and is behind a tuner flag.

Allows the PIP to be dismissed if it is flung towards the bottom center
of the screen and the finger is released within the bottom area of the
screen.

Test: Manual - enable tuner setting, have a PIP, position it at top of
      screen, long- fling it towards bottom center of screen, it dismisses.
Bug: 35358628
Change-Id: I2d3d50093f6523c7bb321e0486dab360095a398e