calendar: added support for custom calendar starting days (#2548)

Closes #2517 

## Description

Added support for custom starting days for calendar.

## Screenshot

| Before                       | After                       |
| ---------------------------- | --------------------------- |
| <img width="395" height="280" alt="image"
src="https://github.com/user-attachments/assets/8926ab0a-d4db-4c50-b100-c5d35c5ffb3c"
/> | <img width="375" height="285" alt="image"
src="https://github.com/user-attachments/assets/4a9235d2-4d29-42e0-8bc5-04774b7eb0d6"
/> |

## How to Test

### First day
                DatePickerState::new(window, cx)
                    .date_format("%Y. %m. %d.")
                    .first_day_of_week(Weekday::Mon)

## Checklist

- [x] I have read the [CONTRIBUTING](../CONTRIBUTING.md) document and
followed the guidelines.
- [x] Reviewed the changes in this PR and confirmed AI generated code
(If any) is accurate.
- [x] Passed `cargo run` for story tests related to the changes.
- [ ] Tested macOS, Windows and Linux platforms performance (if the
change is platform-specific)