async addEditToolbar() {
    if (this._editToolbar || this.#isInEditMode) {
      return this._editToolbar;
    }
    this._editToolbar = new EditorToolbar(this);
    this.div.append(this._editToolbar.render());
    if (this.#altText) {
      await this._editToolbar.addAltText(this.#altText);
    }

    return this._editToolbar;
  }
Add a toolbar for this editor.
@returns {Promise<EditorToolbar|null>}