It's expensive to determine the system time zone from disk each time it
is requested. This makes LibUnicode cache the result, and provides an
API to clear that cache. This will let us set up a monitor to watch for
system time zone changes in platform-dependent ways.
The changes to tests are due to LibTimeZone incorrectly interpreting
time stamps in the TZDB. The TZDB will list zone transitions in either
UTC or the zone's local time (which is then subject to DST offsets).
LibTimeZone did not handle the latter at all.
For example:
The following rule is in effect until November 18, 6PM UTC.
America/Chicago -5:50:36 - LMT 1883 Nov 18 18:00u
The following rule is in effect until March 1, 2AM in Chicago time. But
at that time, a DST transition occurs, so the local time is actually
3AM.
America/Chicago -6:00 Chicago C%sT 1936 Mar 1 2:00
This required updating some LibJS spec steps to their latest versions,
as the data expected by the old steps does not quite match the APIs that
are available with the ICU. The new spec steps are much more aligned.
