Adds the sys_info class and time_zone::get_info(). The code still has a
few quirks and has not been optimized for performance yet.
The returned sys_info is compared against the output of the zdump tool
in the test giving confidence the implementation is correct.
Implements parts of:
- P0355 Extending <chrono> to Calendars and Time Zones
Implements:
- LWGXXXX The sys_info range should be affected by save
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