No Brightness mechanic for VFX

Title. The Brightness Model Mechanic is essential to making good-looking VFX with emissive textures. However, it isn't supported by the actual VFX models.

  - brightness{partid=body;b=15;s=15}

Solution: Either allow all VFX mechanics to also use regular Model mechanics, or add a

  - VFXbrightness{partid=body;b=15;s=15}

mechanic. This would be greatly appreciated.