This is the replacement of the old API with the new API, .timeZoneId and
.getTimeZone(). Semantics will be corrected in the following commit.
Normative PR: https://github.com/tc39/proposal-temporal/pull/2482
This requires a few adjustments of time zone names and offsets in some
places. The only named time zone that is required to be supported by an
implementation not supporting ECMA-402 is "UTC".