PR: Ramps modeled as floors have no base quantities

### Problem Description

Floors exported as ```IfcRamp``` have no BaseQuantities and don't report ```Pset_RampCommon.Slope``` whereas they do when they are exported as ```IfcRampFlight```.

- Tested in 26.4.1 using IFC4RVArch.
- IFC2x3 works fine.

Test model: https://github.com/andydandy74/MyIssues/blob/master/RevitIFC969/131_IFC_FloorAsRamp.rvt

### Revit Version

2026.4.x

### IFC for Revit Addon Version

26.4.1

### Windows Version

11 25H2

Start by reproducing the issue with the linked Revit model using IFC4RVArch, then compare the exported IfcRamp and IfcRampFlight results. Verify the BaseQuantities and Pset_RampCommon.Slope output for IfcRamp, while confirming that the existing IFC2x3 behavior remains unchanged.

Written by the indexing model from the issue text.