Our generator is currently preferring the DST variant of the time zone
display names over the non-DST variant. LibTimeZone currently does not
have DST support, and operates in a mode that basically assumes DST does
not exist. Swap the display names for now just to be consistent until we
have DST support.
Note we will need to generate both of these variants and select the
appropriate one at runtime once we have DST support.
The following table in TR-35 includes a web of fall back rules when the
requested time zone style is unavailable:
https://unicode.org/reports/tr35/tr35-dates.html#dfst-zone
Conveniently, the subset of styles supported by ECMA-402 (and therefore
LibUnicode) all either fall back to GMT offset or to a style that is
unsupported but itself falls back to GMT offset.
This adds an API to use LibTimeZone to convert a time zone such as
"America/New_York" to a GMT offset string like "GMT-5" (short form) or
"GMT-05:00" (long form).
The generator parses metaZones.json to form a mapping of meta zones to
time zones (AKA "golden zone" in TR-35). This parser errantly assumed
this was a 1-to-1 mapping.
