calendar: added support for custom calendar strings, and starting days

[xrtxn]

Closes #2517

Description

Added support for custom weekday, month, and starting days. I found this to be the best tradeoff in terms of performance and ergonomy.

Screenshot

Before	After

How to Test

First day

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

Week day and month day

        .weekday_names([
            t!("calendar.monday"),
            t!("calendar.tuesday"),
            t!("calendar.wednesday"),
            t!("calendar.thursday"),
            t!("calendar.friday"),
            t!("calendar.saturday"),
            t!("calendar.sunday"),
        ])
        .month_names([
            t!("calendar.january"),
            t!("calendar.february"),
            t!("calendar.march"),
            t!("calendar.april"),
            t!("calendar.may"),
            t!("calendar.june"),
            t!("calendar.july"),
            t!("calendar.august"),
            t!("calendar.september"),
            t!("calendar.october"),
            t!("calendar.november"),
            t!("calendar.december"),
        ])

Checklist

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

[huacnlee]

Hi, weekday_names, month_names is not a good solution. I have make change of rust-i18n to support this feature and make PR in #2563

[xrtxn]

Thanks, this should work for me, this was my original idea too, but unsure how to implement it. However, please check out .first_day_of_week() as well, as this is still missing. If you rather I can implement the changes needed for this updated version,

[huacnlee]

first_day_of_week is ok to merge, you can cleanup you PR, then I will merge it.

[xrtxn]

Please check it out, I cleaned up the code