OARIS3 — Replace optional strings with typedefs

The syntax for an optional string (parameter_range: string [0..1]) can cause confusion to parsers of the XMI as to whether the syntax is for being optional or fixed length.
Optional strings would be better defined as an optional TypeDef.

This affects parameter_range and typical_value in the descriptor_type struct within Subsystem_Domain -> Subsystem_Control

Create Typedefs for optional strings

replace the parameters which are of type string [0..1] with typedefs in the descriptor_type class