Revit should export colour information associated to IfcMaterial where possible

Revit seems to want to export colour information using `StyledByItem` (See Geometry presentation assignment in the below chart), whereas although this makes sense in a small subset of scenarios (e.g. object specific colour overrides), for the majority of cases, it makes more sense to assign colours to an IfcMaterial (See material presentation assignment in the below chart).

This leads to extremely unnecessarily large IFC files, as well as confusion when people expect a material to have a colour - and therefore also unnecessarily inefficient workarounds to derive actual colours.


No file, test, or entry point is named. Start by locating the Revit IFC export handling for StyledByItem, IfcMaterial, and material presentation assignment, then compare generated IFC output for ordinary materials and object-specific colour overrides. Done means colours are assigned to IfcMaterial where appropriate without removing valid object-specific overrides, and the resulting IFC files avoid unnecessary duplication.

Written by the indexing model from the issue text.