Limit all "user" properties to be expressed by property sets / remove "direct" attributes

today 98% of all properties that are either set by users in BIM software, or are derived by the software systems based on user entries, are handled by property sets. But there are a few exceptions, like:

- IfcRoot.Name
- IfcRoot.Description
- IfcElement.Tag
- IfcSpatialElement.LongName
- a few more

and there are still many deprecated direct attributes in the schema for backward compatibility issues, like:
- IfcStairFlight.NumberOfRisers, etc.
- IfcMechanicalFastener.NominalDiameter

all those attributes should be removed (or at least repurposed) in order to use only late-binding property sets. The very specific handling of such few attributes makes it already today difficult to use configuration files for IFC mapping of properties in BIM authoring tools.

Start by reviewing the IFC schema definitions for IfcRoot, IfcElement, IfcSpatialElement, IfcStairFlight, and IfcMechanicalFastener, then compare their listed direct attributes with the property-set approach. Done means the scope is resolved for the named and remaining exceptions, including whether each attribute is removed or repurposed.

Written by the indexing model from the issue text.