ST6RI-901 Missing implicit specializations of objects/subobjects

[seidewitz]

This PR corrects missing implicit specializations of Objects::objects and Objects::Object::subobjects in certain cases for port usages and occurrence usages.

1. A nested composite port usage (i.e., a subport) explicitly typed by a port definition meets the criteria for checkFeatureSubobjectSpecialization and, therefore, should have an implied subsetting of Objects::Object::subobject. In particular, Ports::Port::subports should have this implied subsetting, so every subport should then satisfy the constraint automatically. (See also SYSML21-483.)

2. An occurrence usage explicitly typed by a structure type (such as an item definition) meets the criteria for checkFeatureObjectSpecialization (or checkFeatureSubobjectSpecialization, if it is a subobject) and, therefore, should have an implied subsetting of Objects::objects (or Objects::Object::subobjects).