Only set one of customLayout or mediaButtonPreferences

The custom layout is automatically derived from the
button preferences (if non-empty), so there is no need
to set and potentially transfer both.

PiperOrigin-RevId: 828027599

Author: tonihei

libraries/session/src/main/java/androidx/media3/session/MediaSessionLegacyStub.java

@@ -312,12 +312,16 @@ public void setAvailableCommands(
    * the platform session.
    */
   public MediaSession.ConnectionResult getPlatformConnectionResult(MediaSession mediaSession) {
-    return new MediaSession.ConnectionResult.AcceptedResultBuilder(mediaSession)
-        .setAvailableSessionCommands(availableSessionCommands)
-        .setAvailablePlayerCommands(availablePlayerCommands)
-        .setCustomLayout(customLayout)
-        .setMediaButtonPreferences(mediaButtonPreferences)
-        .build();
+    MediaSession.ConnectionResult.AcceptedResultBuilder result =
+        new MediaSession.ConnectionResult.AcceptedResultBuilder(mediaSession)
+            .setAvailableSessionCommands(availableSessionCommands)
+            .setAvailablePlayerCommands(availablePlayerCommands);
+    if (!mediaButtonPreferences.isEmpty()) {
+      result.setMediaButtonPreferences(mediaButtonPreferences);
+    } else {
+      result.setCustomLayout(customLayout);
+    }
+    return result.build();
   }
 
   /**