[libc++][chrono] Loads tzdata.zi in tzdb. - #74928

This implements the loading of the tzdata.zi file and store its contents in the tzdb struct.

This adds all required members except:

• the leap seconds,
• the locate_zone, and
• current_zone.

The class time_zone is incomplete and only contains the parts needed for storing the parsed data.

The class time_zone_link is fully implemented including its non-member functions.

Implements parts of:

• P0355 Extending to Calendars and Time Zones
• P1614 The Mothership has Landed

Implements:

• P1982 Rename link to time_zone_link