See https://github.com/tc39/proposal-temporal/pull/2316 which eliminated
an observable call to Array.prototype[Symbol.iterator]() in the case where
a calendar's 'fields' property was undefined.
The best way I've thought of to test this is to monkeypatch the
Array.prototype[Symbol.iterator]() method to make it throw. In some cases,
where we are actually expected to iterate the return value from a
Temporal.TimeZone's getPossibleInstantsFor() method, we have to provide a
custom method for that as well, that returns a non-Array iterable so we
don't call the patched Array.prototype[Symbol.iterator]().
This normative change reached consensus at the July 2022 TC39 plenary
meeting.
