[C++] Kernel to localize naive timestamps to a timezone (preserving clock-time)

Given a tz-naive timestamp, "localize" would interpret that timestamp as local in a given timezone, and return a tz-aware timestamp keeping the same "clock time" (the same year/month/day/hour/etc in the printed representation). Under the hood this converts the timestamp value from that timezone to UTC, since tz-aware timestamps are stored as UTC.

References: tz_localize in pandas, or force_tz in R's lubridate package

This will (eventually) also have to deal with ambiguous or non-existing times.