Spec text:
https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.era
https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.erayear

Notice this only implement the "iso8601" calendar and we will implement the
code for other calendar later by calling ICU with other Calendar methods.
This CL reduce the differences of testing result between ALWAYS and no_i18n
because the code in no_i18n will not call Calendar era or eraYear and therefore
passed the test even w/o this CL but the ALWAYS tests will cause Temporal
object to internal call era and eraYear and therefore fail if w/o this CL.

Bug: v8:11544
Change-Id: I921fbfbbd26473c238024161eb58b096c38b881b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3641938Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Frank Tang <ftang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80513}