[React] Define defaultProps and PropTypes as static methods in class component

class Toggle extends Component {
  static propTypes = {
    defaultOn: PropTypes.bool,
    on: PropTypes.bool,
    onToggle: PropTypes.func,
    children: PropTypes.oneOfType([
      PropTypes.func,
      PropTypes.array
    ]).isRequired,
  }
  static defaultProps = {
    defaultOn: false,
    onToggle: () => {},
  }
}