Improve polygon offset

[mwestphal]

Context When drawing lines coincident with polygons, there could be z-fighting. We are currently using the default polygon offset value of VTK but I suspect that there is an issue when computing depth range in VTK. Let's investigate.

Steps to reproduce

• download machined-sphere-inside-cube-1.snapshot.4.zip
• `./bin/f3d Ball-Cube.STEP

Notes

more info here: https://gitlab.kitware.com/f3d/f3d/-/issues/217