Implement inset setting for sanding
Implement inset setting for sanding

It keeps a local version of the top surface and modifies it for sanding.

Contributes to issue CURA-3903.

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