SYSML2 — validateDefinitionVariationMembership and validateUsageVariationMembership are too strict

The constraints validateDefinitionVariationMembership and validationUsageVariationMembership require that all the owned members of a variation definition or usage be variant members. This is too strong:

• It disallows any variation Usage from having a Multiplicity, because that is a non-variant owned member of the Usage.
• It disallows a variation PortDefinition from having a required ConjugatedPortDefinition, because that is a non-variant owned member of the definition.

Revise constraints

For both variation definitions and usages, the semantically necessary constraint is really just that the variation not have additional features. Having additional namespace members that are not features is not really a problem. So the constraints can be weakened to only disallow variation definitions and usages from having feature memberships, allowing them to have non-feature memberships. Note that multiplicities and conjugate port definitions are both owned via non-feature memberships, so these would them be allowed (while a multiplicity is a feature, it is not actually featured by its owning feature, but by the featuring types of its owning feature).