Feature request: add a glTF pathtracer

[echadwick-artist]

Could we add a glTF pathtraced renderer to the preview tabs?

A pathtracer would provide an interactive way to compare rasterizers against a ground truth. For example:

(from glTF-Tutorials)

There are several glTF pathtracers available. Three I know about:

• https://dassaultsystemes-technology.github.io/dspbr-pt/
• https://lgltracer.com/viewer/index.html
• https://gkjohnson.github.io/three-gpu-pathtracer/