fix(tts): add missing supported timeline command to TtsSessionAdapter

without this command the session-adapter didn't properly report the current timeline to a media3.MediaSession

Author: ddfreiling

readium/navigators/media/tts/src/main/java/org/readium/navigator/media/tts/session/TtsSessionAdapter.kt

@@ -157,7 +157,8 @@ internal class TtsSessionAdapter<E : TtsEngine.Error>(
                 COMMAND_SET_SPEED_AND_PITCH,
                 COMMAND_GET_CURRENT_MEDIA_ITEM,
                 COMMAND_GET_METADATA,
-                COMMAND_GET_TEXT
+                COMMAND_GET_TEXT,
+                COMMAND_GET_TIMELINE
             ).build()
 
     override fun getApplicationLooper(): Looper {