Resolve a local wall time in an IANA zone to UTC: a repeated one takes the
earlier instant, a skipped one moves forward by the jump. Before 1970 the
shipped tzdb 2025c history answers, loaded by prepareLocalTime (a wall
time before 1970-01-02 throws otherwise); from 1970, and in the fixed Etc
zones, the host's Intl.
Resolve a local wall time in an IANA zone to UTC: a repeated one takes the earlier instant, a skipped one moves forward by the jump. Before 1970 the shipped tzdb 2025c history answers, loaded by
prepareLocalTime(a wall time before 1970-01-02 throws otherwise); from 1970, and in the fixed Etc zones, the host's Intl.