Models for checking normal maps

We need sample models for these cases (+ versions of these with morph targets):

| **Normals** | **Tangents** | **Normal map** | **Engine's feature to check** |
|:-------:|:--------:|:----------:|--------------------------------------------------|
| ❌ | ❌ | ❌ | Flat normals generation |
| ❌ | ❌ | ✔️ | MikkTSpace implementation with generated normals |
| ✔️ | ❌ | ✔️ | MikkTSpace implementation with provided normals |

@bghgary Is it something glTF-Asset-Generator could assist with?

Start with the issue's normals, tangents, and normal-map matrix, then investigate whether glTF-Asset-Generator can produce the requested sample models. Done means providing models for each listed case, including versions with morph targets, so engines can check the corresponding features.

Written by the indexing model from the issue text.