This is a continuation of what's been started in #89178.
As a drive-by, this also changes the PSTL macro to say `EXPERIMENTAL`
instead of `INCOMPLETE`.
This adds the local_info type and its formatting options.
The usage of the local_info object will be done in separate patches.
Implements parts of:
- P0355 Extending to Calendars and Time Zones
- P1361 Integration of chrono with text formatting