MediaRouter: Cleanup MediaRouter2Manager APIs

As a following CL, RoutingController will be removed.
Instead, MediaRouter2Manager will use RoutingSesionInfo.
This CL adds necessary methods for that.

Added Callback#onTransferred and #onTransferFailed.

Bug: 150571233
Test: atest mediaroutertest
Change-Id: If2c23c483f80b6c93a14d1f1f93dfc40463ede1a