Proposed documentation change and rules for IfcOffsetCurveByDistances

In [5.4.3.1](https://standards.buildingsmart.org/IFC/RELEASE/IFC4_3/HTML/lexical/IfcAlignment.htm) IfcOffsetCurveByDistances is described as `IfcOffsetCurveByDistances as a 2D or 3D curve defined relative to an IfcGradientCurve or another IfcOffsetCurveByDistances.`

IfcGradientCurve is 3D so 2D doesn't make sense. Suggest the following:

> IfcOffsetCurveByDistances as a 2D or 3D curve defined relative to an IfcCompositeCurve or IfcGradientCurve, respectively, or another IfcOffsetCurveByDistances.

Proposed rules:

[8.9.3.42 IfcOffsetCurveByDistances](https://standards.buildingsmart.org/IFC/RELEASE/IFC4_3/HTML/lexical/IfcOffsetCurveByDistances.htm)

IfcOffsetCurveByDistance.BasisCurve must be IfcCompositeCurve or IfcGradientCurve.

IfcOffsetCurveByDistance.BasisCurve and all IfcOffsetCurveByDistance.OffsetValues.BasisCurve must be the same curve.