Proposal: CalendarDatePicker with Chinese Lunar Calendar

# Proposal: CalendarDatePicker with Chinese lunar calendar

## Summary
In China, the lunar calendar is also a very common calendar. I hope to add the lunar date below the date of the CalendarDatePicker and CalendarView configured for the Chinese region.

## Rationale

* Most Chinese calendars display lunar dates.
* Windows Calendar provide Chinese lunar calendar.

Start by locating the CalendarDatePicker and CalendarView implementations and reviewing how they handle region-specific date display. Define the Chinese-region behavior and identify the calendar support needed before implementation. Done means both controls show the corresponding Chinese lunar date below the regular date, with coverage for that behavior.

Written by the indexing model from the issue text.