The guest local tick was decoded into a DateTimeKind.Utc DateTime and then
passed to TimeZoneInfo.ConvertTimeToUtc together with TimeZoneInfo.Local.
That overload throws ArgumentException when a Utc-kind value is paired with a
source zone other than UTC, so on any machine whose local zone is not UTC the
export caught the exception and always returned INVALID_ARGUMENT.
Re-tag the decoded value as DateTimeKind.Unspecified so it is interpreted as
local wall-clock time and converted correctly. The reverse direction
(sceRtcConvertUtcToLocalTime) was already correct because ConvertTimeFromUtc
accepts a Utc-kind input.
Add a RtcExports unit-test suite covering the tick/calendar conversions, DOS
time packing, Win32 file time, leap-year and validation error codes, and a
regression test that round-trips a UTC tick through local time and back.
