Media: Introduce MediaRouter2

Instead of extending MediaRouter, this CL introduce MediaRouter2 class.
This will prevent regression from chaing MediaRouter and we can easily
modify and test `new' features.
For MediaRouter2, IMediaRouter2Client is also added to differentiate the
previous router and the new one in MediaRouterService.

This CL also contains MediaRouter2.sendControlRequest which can be used
to manipulate media routes.
(It is temporarily being used to test MediaRouter2Manager callbacks.)

Bug: 132138073
Test: atest mediaroutertest (w/ mediarouteprovider installed)

Change-Id: I895fe456e38d437cec8e3ca9501cd7f105c5f4d6