feat: PolygonPointer as distinct from PolygonRef (CURA-2602)
feat: PolygonPointer as distinct from PolygonRef (CURA-2602)

It was a bad idea to change PolygonRef into PolygonPointer, because then we'd have to check whether it is a nullptr all over the engine...

alephobjects/CuraEngine,Ultimaker/CuraEngine,Ultimaker/CuraEngine,ROBO3D/CuraEngine,ROBO3D/CuraEngine,alephobjects/CuraEngine,alephobjects/CuraEngine,ROBO3D/CuraEngine