Allow Pset_ConstructionOccurence to also be used on IfcGroup for Systems

In Asset Management Registers there is a need to uniquely identify not just the actual individual, but also it’s sub- and main system. By allowing the use of Pset_ConstructionOccurence also on the actual system it belongs to it would give the asset manager the possibility of having one single Pset for identifying it's assets.

Example:
An IfcLightFixture _AB+2111K=631BA090_
Fitted on IfcMember.POST _AB+2111K=631PS090_
add a few IfcPipeSegment.FLEXIBLESEGMENT and you have a circuit (or a group) _AB+21184=631WC001-7_
then add to this the Mains cabinet IfcElectricDistributionBoard.SWITCHBOARD _AB+21184=631WC001

They all belong to an IfcDistributionSystem.LIGHTING **_V=C.VS=QGA.EA001_**


Start by reviewing the IFC schema definitions and usage rules for Pset_ConstructionOccurence, IfcGroup, and IfcDistributionSystem. Compare the asset and system examples in the issue, then determine the schema changes and validation needed so the property set can identify the relevant group and system consistently.

Written by the indexing model from the issue text.