Added simple operator to add transition between two mep segments (now only rectangular collinear segments are supported).
It also reuses the transition type that was previously used to connect segments of the same type.
Demonstration - https://imgur.com/a/c1AOxj1
Now blender curves segments saved in IfcIndexedPolyCurves instead of creating individual polygons.
Also changed ShapeBuilder.polyline - now it will try to store points in IfcLineIndex where it's possible (previously it was storing just 2).
Error occured because ShapeBuilder was assigning "Curve2D" representation type for elevation view curves when the correct type is "Curve3D".
It use to occur for both doors and windows created with ifc modifier.
```
Validation error text:
2023-04-03:18:21:28,879 ERROR [rule_executor.py:154] On instance:
#135=IfcShapeRepresentation(#21,'Profile','Curve2D',(#134))
Rule IfcShapeRepresentation_CorrectItemsForType:
(IfcShapeRepresentationTypes(self.RepresentationType,self.Items))
Violated by:
False
+ where False = IfcShapeRepresentationTypes('Curve2D', (#134=IfcIndexedPolyCurve(#133,(IfcLineIndex((1,2)),IfcLineIndex((2,3)),IfcLineIndex((3,4)),IfcLineIndex((4,1))),$),))
+ where 'Curve2D' = #135=IfcShapeRepresentation(#21,'Profile','Curve2D',(#134)).RepresentationType
+ and (#134=IfcIndexedPolyCurve(#133,(IfcLineIndex((1,2)),IfcLineIndex((2,3)),IfcLineIndex((3,4)),IfcLineIndex((4,1))),$),) = #135=IfcShapeRepresentation(#21,'Profile','Curve2D',(#134)).Items
```