function toRegExp(string) {
  const parts = RE_REGEXP_STR.exec(string)
  if (parts) {
    return new RegExp(parts[1], parts[2])
  }
  return new RegExp(`^${escape(string)}$`)
}
Convert a string to the `RegExp`.
Normal strings (e.g. `"foo"`) is converted to `/^foo$/` of `RegExp`.
Strings like `"/^foo/i"` are converted to `/^foo/i` of `RegExp`.

@param {string} string The string to convert.
@returns {RegExp} Returns the `RegExp`.