Media : Implement getAvailableRoutes in MediaRouter2Manager

This CL adds capability to media route 2 info, which can be used
to get available routes for each app, which set control categories.

The test for control category is changed to test getAvailableRoutes().

Test: atest mediaroutertest

Change-Id: If93d64f02b4868b5e04b737431291b18a52177de