static parseFormatForOpts(formatOpts, localeOpts = {}) {
    const tokenList = formatOptsToTokens(formatOpts, Locale.fromObject(localeOpts));
    return !tokenList ? null : tokenList.map((t) => (t ? t.val : null)).join("");
  }
Produce the format string for a set of options
@param formatOpts
@param localeOpts
@returns {string}