Add veil for swap animations when insets are in play

This CL adds the ability for SplitDecorManager to add a veil (with icon) when a swap animation is playing, if there are insets that would necessite a redraw at the end of the swap. (e.g. swapping vertically when there is an inset on the top/bottom).

It also removes the "screenshot" layer for split swaps, instead opting to achieve the same effect by removing window focus-ability during the animation.

Fixes: 291893598
Test: Visually confirmed in a variety of orientations, slowdowns, and input cases
Flag: EXEMPT bugfix
Change-Id: Ic34bf8c1f8eecb42fe4589b54f23558f2d0a5fe7