onHandleCode(code, filePath) {
    const ev = new PluginEvent({code});
    ev.data.filePath = filePath;
    this._execHandler('onHandleCode', ev);
    return ev.data.code;
  }
handle code.
@param {string} code - original code.
@param {string} filePath - source code file path.
@returns {string} handled code.