Add direct reference in IfcBuildingElementProxy to use IfcBuiltElement as an arbitrary built element

[fg55b]

Greetings!

There is a note in IfcBuiltElement specifying that "It is advised not to use IfcBuildingElementProxy to represent an arbitrary built element, but to use a direct instantiation of IfcBuiltElement instead.".

Since the IfcBuildingElementProxy was used as a general built element until IFC version 4.3, adding a direct reference to this change in its documentation — perhaps using the same note found in IfcBuiltElement — could help users easily identify this update.

Additionally, are there any uses for IfcBuildingElementProxy that cannot be accomplished with a direct instantiation of IfcBuiltElement?