Select exolist-specified subtitles by default

If a sample has a subtitle file listed, it makes sense to show it by
default.

PiperOrigin-RevId: 277934597

demos/main/src/main/java/com/google/android/exoplayer2/demo/PlayerActivity.java

@@ -436,7 +436,7 @@ public class PlayerActivity extends AppCompatActivity
             Format.createTextSampleFormat(
             Format.createTextSampleFormat(
                 /* id= */ null,
                 /* id= */ null,
                 subtitleInfo.mimeType,
                 subtitleInfo.mimeType,
-                /* selectionFlags= */ 0,
+                C.SELECTION_FLAG_DEFAULT,
                 subtitleInfo.language);
                 subtitleInfo.language);
         MediaSource subtitleMediaSource =
         MediaSource subtitleMediaSource =
             new SingleSampleMediaSource.Factory(dataSourceFactory)
             new SingleSampleMediaSource.Factory(dataSourceFactory)