b5f2db9406
This adds a subset of the C++20 calendar data formatters: - day, - month, - year, - month_day, - month_day_last, and - year_month_day. A followup patch will add the missing calendar data formatters: - weekday, - weekday_indexed, - weekday_last, - month_weekday, - month_weekday_last, - year_month, - year_month_day_last - year_month_weekday, and - year_month_weekday_last.