The Etc/GMT±... time zones should be accepted in from() as well as the
TimeZone constructor. Previously this was not the case for +0 and -0 due
to those being IANA legacy names.
This basically copies the existing test file for the TimeZone constructor,
and performs the same tests for TimeZone.from().
See https://github.com/tc39/proposal-temporal/pull/2292 which is a
normative change that achieved consensus at the July 2022 TC39 meeting.
