Simplification should recognize and handle UV mirroring seams

[Makio64]

Rare case but on some models, simplification lead to UV artefacts : UVs are getting fully streched (same value on both vertices) when many other triangles could have been optimized instead, I suggest to give a lower priority to simplify/remove vertices/faces of the mesh leading to these results.

It might also be a bug in the way the uvs get re-assigned.

The model used to illustrate this example :
https://www.dropbox.com/scl/fi/po761ykdiqdmtbzd9fitf/rhino.glb?rlkey=s6jp06vtr4id0opnv76wwys1p&dl=0

Before simplify :

After simplify :

[zeux]

Are UVs mirrored here? If so then yeah it’s a known issue atm, and will get addressed eventually.

[zeux]

Yeah I looked at the scene closer and it's indeed UV mirroring. This needs special handling in the simplifier, probably as a separate pre-process.

Re-attaching the file so that this isn't lost in the future (I also regenerated the normals here because they were just broken in the input file):
rhino.zip
rhino-tbn.zip

Worth noting is that if the GLB file gets re-exported with tangent data and a normal map (without a normal map gltfpack needs -kv flag), the simplifier will automatically recognize the mirroring seam and simplify correctly (of course, this ideally should work without tangent information present to begin with):