Don't animate move triggered by resizing using dock divider.

Also includes some small, nice refactoring:
* move code that sets the move animation into WindowStateAnimator;
* a few fields can be made private in WindowStateAnimator this way;
* one boolean flag in WindowStateAnimator popped out as unused after
being privatized, so could be deleted.

Bug: 25690109
Change-Id: I8144114244892c4f27aff21455e8e76eddbd039f