MediaRouter2: Revise MediaRouter2.Callback.onRoute**

This CL revised callbacks for MediaRouter2 so that it gives
a list instead of a single route.
This will effectively reduce the number of invokings.

This CL also fixes binder call between media router service and media
router such that media router service notifies only changes of routes
instead of all provider information.

Following CLs will update manager callbacks as well.

Test: atest mediaroutertest
Change-Id: Ibbc23aa5f12f5450d44c81756e3fcefe3e0d7f4b