message: Add getter for DisplayObject destroyed
diff: @@ -450,6 +450,14 @@ export abstract class DisplayObject extends EventEmitter
  * @event destroyed
  */
  + /**
  + * Readonly flag for destroyed display objects.
  + */
  + get destroyed(): boolean
  + {
  + return this._destroyed;
  + }
  +
  /**
  * Recalculates the bounds of the display object.
  */
  