It's no longer possible to fake built-in time zones using custom objects.
So testing DST shifts will have to use real built-in time zones. Replace
TemporalHelpers.springForwardFallBackTimeZone with America/Vancouver (it
was modelled on the DST transitions in 2000) and
TemporalHelpers.crossDateLineTimeZone with Pacific/Apia (it was modelled
on the 2011 switch to the other side of the international date line.)
These tests have to move to the intl402/ folder since non-Intl-aware
implementations are allowed (but not required) to support any built-in
time zones other than UTC.
