MediaRouter: Introduce discovery request

Providers are notified of change of discovery request
to respond properly.

Whenever a media app registers a callback it should provide
discovery request which includes route types and a way to scan.

MediaRouter combines all discovery request into a single request
and sends it to the media router service, which combines requests
from all clients and notifies provider of the combined request.

This CL also changes control category as route type.

Bug: 139033746
Test: atest mediaroutertest
Change-Id: I5ca37683ae0761ff587c1c920e32fd6d768a2cd3
diff --git a/services/core/java/com/android/server/media/MediaRoute2Provider.java b/services/core/java/com/android/server/media/MediaRoute2Provider.java
index 55c4e21..9ca302e 100644
--- a/services/core/java/com/android/server/media/MediaRoute2Provider.java
+++ b/services/core/java/com/android/server/media/MediaRoute2Provider.java
@@ -46,7 +46,7 @@
     }
 
     public abstract void requestCreateSession(String packageName, String routeId,
-            String controlCategory, long requestId);
+            String routeType, long requestId);
     public abstract void releaseSession(int sessionId);
 
     public abstract void selectRoute(int sessionId, String routeId);