Add mesh cleanup operator

[jlampel]

In v3 we had operators under Target Cleaning for snapping the verts to the surface, merging by distance, recalculating the normals, and flipping bad symmetry.

In v4, I think we can just have a single operator that can run all of the cleanup operations at once, with options for which ones are taken into account.

Having this as one-click and easily accessible is important since many of Blender's modeling features do not automatically snap to the surface, and we cannot write custom versions of every tool. Perhaps in the future this could be automatically run after certain non-RF tools are used.