Put PIP windows above transition animations.

PIP activities are already on top of everything else, but during
animation we increase the layer of the animated window for the duration
of the animation and it may cover the PIP. By forcing the same
adjustment on PIP windows we will keep them above animating windows.

Bug: 26015827
Change-Id: I8f7a87f41fed24b3e520fb599a94cf24cc2eeb50