Add C++ and QML API for country, country subdivision and timezone lookups

This attempts to unify various bits of code and translations related to countries and timezones all over the place.

iso-codes is used for the country and country subdivision translations, two OSM-based datasets are used for the geographic lookup tables and their timezone <-> country mappings. Substantial parts of the code are based on existing similar solutions in KContacts and KItinerary.

See also:

• https://phabricator.kde.org/T12429
• https://volkerkrause.eu/2021/05/22/kf5-iso-codes-api.html
• https://volkerkrause.eu/2021/07/10/kf5-timezones-per-country.html
• https://volkerkrause.eu/2021/07/24/kf5-country-timezone-location-lookup.html

Still missing in this context (see T12429 on what blocks this):

• timezone translations
• country -> language lookup and language name translations

This can be added on top of this though, and shouldn't block the integration of the already working parts.