Always reset the Gregorian change date, because all uses either require the
Gregorian change date to be set to `-8.64e15` or don't care about dates far
into the past.
The slow `DateIntervalFormat::TryFormatCalendar` is now only used when
`MOZ_SYSTEM_ICU` is defined.
And also resets the Gregorian change date for "buddhist", "japanese", and
"roc" to get consistent results when compared to the ICU4X-based Temporal
code.
Differential Revision: https://phabricator.services.mozilla.com/D241644
472da3bb00