Add @IntDef annotations to DefaultEventListener

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=170980737

library/core/src/main/java/com/google/android/exoplayer2/Player.java

@@ -169,7 +169,7 @@ public interface Player {
     }
 
     @Override
-    public void onRepeatModeChanged(int repeatMode) {
+    public void onRepeatModeChanged(@RepeatMode int repeatMode) {
       // Do nothing.
     }
 
@@ -184,7 +184,7 @@ public interface Player {
     }
 
     @Override
-    public void onPositionDiscontinuity(int reason) {
+    public void onPositionDiscontinuity(@DiscontinuityReason int reason) {
       // Do nothing.
     }