Resize all changed windows and fix moveTaskToStack

- Add all changing windows to mResizingWindows when an ActivityStack
is resized.

- Stop calling TaskStack.setBounds if the bounds haven't changed.

- Make moving a task from one stack to another work properly.

- Eliminate unused methods and redundant variables in WindowState and
WindowStateAnimator.

Change-Id: I3a950c777bcc50cdeced150d44423d4d0b38af4a