TabController.animateTo() should return future like ScrollController.animateTo() #19143
Description
ScrollController.animateTo() returns a Future, so that I can easily animate a scroll change, and then do something when we've arrived.
TabController.animateTo() is void, so I can't.
I would like these to have a more consistent signature, and I'd like to be able to easily do something after a TabController's animateTo has completed.