LibTimeZone: Parse and generate a list of time zones used by region

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.

Userland/Libraries/LibTimeZone/TimeZone.cpp

@@ -192,4 +192,8 @@ Optional<Location> get_time_zone_location(StringView time_zone)
     return {};
 }
 
+Optional<Region> __attribute__((weak)) region_from_string(StringView) { return {}; }
+StringView __attribute__((weak)) region_to_string(Region) { return {}; }
+Vector<StringView> __attribute__((weak)) time_zones_in_region(StringView) { return {}; }
+
 }