static normalizeZone(input) {
    return normalizeZone(input, Settings.defaultZone);
  }
Converts the input into a {@link Zone} instance.

* If `input` is already a Zone instance, it is returned unchanged.
* If `input` is a string containing a valid time zone name, a Zone instance
  with that name is returned.
* If `input` is a string that doesn't refer to a known time zone, a Zone
  instance with {@link Zone#isValid} == false is returned.
* If `input is a number, a Zone instance with the specified fixed offset
  in minutes is returned.
* If `input` is `null` or `undefined`, the default zone is returned.
@param {string|Zone|number} [input] - the value to be converted
@return {Zone}