presto-main/src/main/java/io/prestosql/operator/scalar/DateTimeFunctions.java/DateTimeFunctions/timestampAtTimeZone
class DateTimeFunctions:    @ScalarFunction("at_timezone")
    @LiteralParameters("x")
    @SqlType(StandardTypes.TIMESTAMP_WITH_TIME_ZONE)
    public static long timestampAtTimeZone(@SqlType(StandardTypes.TIMESTAMP_WITH_TIME_ZONE) long timestampWithTimeZone, @SqlType("varchar(x)") Slice zoneId)
    {
        return packDateTimeWithZone(unpackMillisUtc(timestampWithTimeZone), zoneId.toStringUtf8());
    }