KERML_ — MultiplicityRanges should allow owned members other than bounds

The abstract syntax for MultiplicityRange specifies that bound redefines ownedMember (see 8.3.4.11.2). However, the concrete syntax production for MultiplicityRange (see 8.2.5.11) allows it to have a TypeBody, which can include additional ownedMembers than the bounds. Indeed, the MultiplicityRanges declared in the Base library model have bodies with documentation comments, which are ownedMembers in addition to the declared bounds.

Update MultiplicityRange abstract syntax

1. Update the abstract syntax for MultiplicityRange so that bound subsets ownedMember, rather than redefining it.
2. Revise the derivation constraints for lowerBound and upperBound.
3. Add a derivation constraint for bound.
4. Add a validation constraint to ensure that the bound Expressions are the first ownedMembers of a MultiplicityRange.