UserDefinedType serialization should be strongly typed

UDT's serialize method takes an Any rather than the actual type parameter. The issue lies in CatalystTypeConverters convertToCatalyst(a: Any): Any method, which pattern matches against a hardcoded list of built-in SQL types.

Planned fix is to allow the UDT to supply the CatalystTypeConverter to use via a new public method on the abstract class UserDefinedType that allows the implementer to strongly type those conversions