This commit moves the length calculations out to be directly on the
StringView users. This is an important step towards the goal of removing
StringView(char const*), as it moves the responsibility of calculating
the size of the string to the user of the StringView (which will prevent
naive uses causing OOB access).
The zone1970.tab file in the TZDB contains regional time zone data, some
of which we already parse for the system time zone settings map.
This parses the region names from that file and generates a list of time
zones which are used in each of those regions.
This renames the current implementation of current_time_zone to
system_time_zone to more clearly indicate what it is. Then reimplements
current_time_zone to return whatever was set up by tzset, falling back
to UTC if something went awry, for convenience.
This changes LibTimeZone to read the current time zone from the file
/etc/timezone rather than using tzset/tzname. Instead, in a subsequent
commit, LibC's time methods will be changed to used LibTimeZone to
retrieve the system time zone.
Also add an API to set the system time zone. This method is only allowed
when running within Serenity.
If the tzname is unknown, fall back to UTC for now. Unknown time zones
are most likely due to not parsing RULE entries yet, but at the very
least, it only makes sense for current_time_zone to return a time zone
that LibTimeZone actually knows about.
Instead of only having dummy functions that don't work with any input,
let's at least support one time zone: 'UTC'. This matches the basic
Temporal implementation for engines without ECMA-262, for example.
This is a rather naive implementation, but serves as a first pass at
determining the GMT offset for a time zone at a particular point in
time. This implementation ignores DST (because we are not parsing any
RULE entries yet), and ignores any offset patterns of the form "Mon>4"
or "lastSun".
