Fixed bug where stack crop wasn't applied when it should

- Apply stack crop if window isn't animating when replacing window.
We were previously not applying the crop if replacing window regardless
of the animation state.
- Apply stack crop if the current docked window isn't animating.
We were previously not applying if any window in the system is animating.
- Also created setter/getter methods for WindowAnimator.mAnimating
to make debugging easier.

Bug: 25645069
Change-Id: I671549626e218358a7dea9e78bd0b2a1f1b3a51e