Makes model substitution (VRML->STEP in STEP Export) optional. This can
prevent nasty surprises where the user doesn't see/can't affect the
outcome
Also, when substituting models, do not maintain scale factor. So a VRML
model with non-unity scaling will not be export as a STEP file (of the
same name) with non-unity scaling. This is the first step to address
https://gitlab.com/kicad/code/kicad/-/issues/1781
- The default value is 0.01 mm (according to comments and similar to the 3D viewer
settings that uses 0.02 mm)
- The export dialog has now 3 values 1 micron, 0.01mm (default) and 0.1 mm
The 0.1 micron option is removed: it makes no sense for a mechanical tolerance.