Fix vertices export with multiple attributes

[Brachi]

Vertices are not exported correctly, causing visual artifacts in-game around UV seams.
The work-around is to use the "Fix leaked textures" tool from Albam Reloaded that essentially splits vertices in the UV edges.
This shouldn't be necessary if the exporter would generate the extra vertices at export time. Touching the original mesh or a copy of it shouldn't be necessary
This happens because GPUs expect that each new vertex attribute be a different item in in the vertices array. That's why an imported model always has duplicate vertices that can be removed with the "Merge by distance" operator.
See the official Blender glTF importer/explanation in the "Merge vertices" tooltip for import:

the glTF format requires discontinuous normals, UVs, and other vertex attributes to be stored as separate vertices, as required for rendering on typical graphics hardware. This option attempts to combine co-located vertices where possible.

The glTF exporter splits the vertices automatically, so it can be used as a reference. Handling triangle strips (RE5) when performing the split seems like a challenge and prevented this to be implemented so far.