Converts a date/time, which is interpreted as local time in this time zone, into UTC. Because of daylight savings time shifts, the date/time may occur twice. In such cases, this method returns the UTC time for the first occurrence. If you need the UTC time of the second occurrence, use offsetAtZoneTime(). name="zoneDateTime" local date/time. An error occurs if zoneDateTime.timeSpec() is not Qt.LocalTime.