static monthsFormat(
    length = "long",
    { locale = null, numberingSystem = null, locObj = null, outputCalendar = "gregory" } = {}
  ) {
    return (locObj || Locale.create(locale, numberingSystem, outputCalendar)).months(length, true);
  }
Return an array of format month names.
Format months differ from standalone months in that they're meant to appear next to the day of the month. In some languages, that
changes the string.
See {@link Info#months}
@param {string} [length='long'] - the length of the month representation, such as "numeric", "2-digit", "narrow", "short", "long"
@param {Object} opts - options
@param {string} [opts.locale] - the locale code
@param {string} [opts.numberingSystem=null] - the numbering system
@param {string} [opts.locObj=null] - an existing locale object to use
@param {string} [opts.outputCalendar='gregory'] - the calendar
@return {Array}