Duplicate Vertices in VNFs not allowed with Manifold

[adrianVmariano]

From https://github.com/openscad/openscad/issues/5134

"What changed in OpenSCAD lately is that we moved away from using "polygon soups" as an internal format, and we now use indexed polygon meshes. Each topological vertex must be specified at one unique index. If you specify the same vertex position twice, it's treated as two separate vertices, and you must hence construct a mesh to account for that."

This seems like it will affect a lot of the nontrivial closed VNF constructions in BOSL2. It's not clear how we can address this without a massive slowdown from constantly running vnf_merge_points().

Like have VNFs also carry an edge list to reduce the number of vertices that need to be checked when joining VNFs?