Implement Temporal.PlainMonthDay.prototype.toLocaleString

[jedel1043]

Spec: https://tc39.es/proposal-temporal/#sec-temporal.plainmonthday.tolocalestring

[alienx5499]

Hi @jedel1043,

I’d like to work on this.

I’m currently implementing Temporal.PlainYearMonth.prototype.toLocaleString in #5098 using the shared format_date_time_locale pipeline introduced in #5080.

Once that lands, I plan to implement Temporal.PlainMonthDay.prototype.toLocaleString using the same approach.

If that sounds good, please feel free to assign this issue to me.

Thanks!

[Cypher-CP0]

Hi, I'd like to work on this. After reading the codebase, I see that the existing format_date_time_locale in date_time_format/mod.rs operates on Unix timestamps, which means it can't directly handle PlainMonthDay (no year/timezone). My plan is to add a new format_plain_month_day_locale function there that uses ICU4X to format month+day fields directly, then call it from plain_month_day::to_locale_string. Does this align with how you'd like it implemented? Happy to start a draft PR.