Media: Introduce MediaRouter2Service

Implementations related to MediaRouter2 and MediaRouter2Manager are
moved to MediaRouter2Service to differentiate it and the previous
implementation.

Once MediaRouter2Service is finished, either it is merged to
MediaRouterService or it will replace MediaRouterService.

Bug: 130848964
Test: manually test cast using system ui and settings

Change-Id: I1360977e2c241e21c14c7fb5f705b77a3e3a85ac