message: adding implicit end attribute to StateTimeline
  used when the ending is impilcitly scheduled as in Player
diff: @@ -7,6 +7,11 @@ export interface StateTimelineEvent extends TimelineEvent {
  state: PlaybackState;
  duration?: Seconds;
  offset?: Seconds;
  + /**
  + * Either the buffer is explicitly scheduled to end using the stop method,
  + * or it's implicitly ended when the buffer is over.
  + */
  + implicitEnd?: boolean;
  }
  /**
  