function formatOffset(formatFn, date, format, timezone) {
  if (timezone === currentTimezone()) {
    return formatFn(date, format);
  }
  if (timezone === 'UTC') {
    return `${formatFn(offsetDate(date, 'UTC').date, format)} UTC`;
  }

  if (shouldHandleTimezone(timezone)) {
    const offset = offsetDate(date, timezone);
    return `${formatFn(offset.date, format)} ${offset.abbr}`;
  }
  else {
    return formatFn(date, format);
  }
}
Pass a format function to format within a timezone.
@param {Function} formatFn - The format function to use.
@param {Date|string} date - The date to format.
@param {string} format - The format to format the date to.
@param {string} timezone - The timezone to format the date to.
@returns {string} - The formatted date.