SDMN — MultiplicityKind - replace with enum

Proposed change

The possible values of MultiplicityKind can be (and are) exhaustively definable. It would be more easily expressed as an enum type, and its use elsewhere in the model should be replaced by that enum type.

Change MultiplicityKinds into an Enumerated Set and Review the types of that set

Change MulitplicityKinds into an Enumerated Set, instead of a vocabulary list, and Review the types of that set.

Also, remove Section 12.2 - MultiplicityKind - from the Vocabularies section. Since ItemKind is also being removed by SDMN-99, delete Section 12 - SDMN Library - completely
Replace Section 10.2.3 - MultiplicityKind - with the definition of the enumerated list instead of the vocabulary