function ElementRegistry(eventBus) {

  /**
   * @type { {
   *   [id: string]: {
   *     element: ElementLike;
   *     gfx?: SVGElement;
   *     secondaryGfx?: SVGElement;
   *   }
   * } }
   */
  this._elements = {};

  this._eventBus = eventBus;
}
A registry that keeps track of all shapes in the diagram.

@class
@constructor

@param {EventBus} eventBus