Previously, the "Simplify" option was a world space distance threshold.
This meant that zooming in and out of the view changed the way
this option behaved. There were complaints from artists about this.
This change improves two things:
* The simplify algorithm uses the screen space coordinates rather than the
3D positions.
* The UI setting is in pixels making it much easier to tweak (no need
for values in the 1e-4 range).
Pull Request: https://projects.blender.org/blender/blender/pulls/122719
a40a4ccb2f