Rename selectRoute(String, MediaRoute2Info) to transfer()

The new method represents the real underlying operation, which is a
routing session transfer to a different device. The appropriate method
for route selection is selectRoute(RoutingSessionInfo, MediaRoute2Info).

This change is a non-functional refactor.

Bug: 238178508
Bug: 205124386
Test: atest CtsMediaBetterTogetherTestCases MediaDeviceTest
MediaRouter2Manager InfoMediaManagerTest

Change-Id: Ic199686849365138049ccb73189bbc03703117b1