Implement UDF to interpret date/timestamp using its internal representation and Gregorian-Julian hybrid calendar

UDF that converts a date/timestamp to new proleptic Gregorian calendar (ISO 8601 standard), which is produced by extending the Gregorian calendar backward to dates preceding its official introduction in 1582, assuming that its internal days/milliseconds since epoch is calculated using legacy Gregorian-Julian hybrid calendar, i.e., calendar that supports both the Julian and Gregorian calendar systems with the support of a single discontinuity, which corresponds by default to the Gregorian date when the Gregorian calendar was instituted.