MediaRouter2: Updates callback for MediaRouter2Manager

This CL updates callbacks for MediaRouter2Manager such that
onRoutesAdded, onRoutesRemoved are added and onRoutesChanged is changed.

onControlCategories also is added to know when getAvailableRoutes() can
be called.

It also updated tests for that and add some helper methods to test
easily.

Test: atest mediaroutertest

Change-Id: I122ce8f8472e01284f13b8aec79e3b8e97fc712b