async get(name) {
    if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
      throw new Error("Not implemented: get");
    }
    await this.#initializedPromise;
    return AppOptions.get(name);
  }
Get the value of a preference.
@param {string} name The name of the preference whose value is requested.
@returns {Promise} A promise resolved with a {boolean|number|string}
                   containing the value of the preference.