Pinned stack animation: Also clear finalClipRect.

The code calculating it doesn't understand our scaling of Surface insets
and so it clips us too small. Since we scale to the stack bounds anyway
there is no sort of "draw over other apps" risk.

Bug: 35396882
Test: Move skeleton pip activity between states, ensure there are no cut off portions during animation.
Change-Id: I973db1879dd588d829e3fe828e9350f2647cdc2c