SYSMLR — Make ItemFlow a specialization of DirectedRelationshipPropertyPath

Issue:
When ItemFlow connects (deeply) nested or inherited properties (e.g. ports or parts) we cannot uniquely identify the sources and targets in its context.

Description:
This is similar to other relationships which specialize DirectedRelationshipPropertyPath, e.g. "The Allocate stereotype
specializes DirectedRelationshipPropertyPath to enable allocations to identify their sources and targets by a multi-level path of accessible properties from context blocks for the sources and targets."

The DirectedRelationshipPropertyPath stereotype based on UML DirectedRelationship.
Stereotype <<ItemFlow>> extends UML metaclass UML4SysML::InformationFlow which specializes DirectedRelationship.

This Issue was not resolved in this Task Force and was automatically deferred to the next Task Force