Fix vertices with different texture coordinates in imported models getting collapsed

[davepagurek]

Resolves #6921

Changes

Previously, when importing models, p5.Geometry vertices were being reused whenever a vertex position + material gets reused in the OBJ code. However, vertex position + color alone are not all that's included in p5.Geometry vertices: it also includes texture position and normals. By not accounting for this, some vertex texture coordinates were being collapsed, leading to interpolation of textures and normals where there should be a seam.

Screenshots of the change

https://editor.p5js.org/davepagurek/sketches/Y1ui2XK_n

PR Checklist

• npm run lint passes
• [Inline documentation] is included / updated
• [Unit tests] are included / updated

[Qianqianye]

Thanks @davepagurek!