refactor: made infill generation functions non-static (CURA-401)
refactor: made infill generation functions non-static (CURA-401)

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