[lldb][libc++] Adds some C++20 calendar data formatters. (#76983)

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.