PBRGraph shader does not work for points topology

[hybridherbst]

Describe the bug 💬

The attached model has some points topology in it.
Unity tries to render it, but fails with a shader error:

Drawing with MeshTopology.Points, yet the vertex program 'UnityGLTF/PBRGraph' does not have PSIZE output.

I think that points should probably be rendered with a custom unlit shader that supports map + color + vertex color (lighting on them doesn't really make sense), but care has to be taken to ensure compatibility with BiRP, URP, HDRP.

Steps to reproduce 🔢

1. Download 20250223-MixedTopologySphere.glb.zip
2. Import in Unity at edit time

Files to reproduce the issue ♻

No response

Editor Version 🎲

2021.3

Render Pipeline and version

URP

UnityGLTF Version

2.14

Operating System 👩‍💻

macOS

When does this problem happen?

• Editor Import
• Runtime Import
• Editor Export
• Runtime Export

Additional Info 📜

Related: atteneder/glTFast#246

Validations 🩹

• I have searched existing issues: no issue already exist that reports the same problem.
• I follow the Code of Conduct
• I provided a minimal reproducible example, including files when necessary.