The typical use case is as follows: a client asks for a collection of model elements of some kind (e.g. class members),
then it enumerates the collection to process elements of the given kind (for example, functions).

Now the entire collection of the elements is created (requested from persistence) at once. But UIDs contain enough
information to understand the kind of the elements.

So it's worth adding methods that receive an array of kinds (CsmDeclaration.Kind).
For example, in CsmClass, apart from
Collection<CsmMember> getMembers
add
Collection<CsmMember> getMembers(CsmDeclaration.KIND kinds...)