Support running AVD on UI thread

By default, AVD animates on RT thread. But since in some cases there's a
need for a finer control on when the frame update for the animation should
happen, such as coordiating the AVD animation with other animations that
run on UI thread, we are providing a way to force the AVD to run on UI
thread.

Bug: 27278616
Change-Id: I372ecd3dc52e3fa0bdce3a1e9c19443f9b199027