Fix freeform to recents animating window being cuttoff.

The window will appear cutoff during the animation if the window was
cropped due to stack or decor bounds before the animation started. We
need to disable the cropping (both from decor and from stack bounds)
for the duration of the animation.

Unfortunately, by disabling cropping of a freeform window to the stack
bounds, we will make it appear above the docked window during the
animation (because the animation will lift the layer). To fix this, we
need to treat the docked stack like the pinned stack and assume it's
always on top for the layering purposes.

CL also includes refactoring of mSystemDecorRect and
mLastSystemDecorRect which can be moved from WindowState to
WindowStateAnimator and made private there.

Bug: 24913782
Change-Id: Idbea99ba04e9449d0563d0c02636f8b4b63087f7