Spec Text:
https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.monthcode

Note- this is only the non-intl version. intl version in
https://tc39.es/proposal-temporal/#sup-temporal.calendar.prototype.monthcode
will be implemented in later cl.

Bug: v8:11544
Change-Id: I52dfc1bda6d2ed8c0aba735c64d7ae8227844ed1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3531555Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Frank Tang <ftang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80348}