Example: Add 3D LUT Color Grading Postprocessing Pass

[gkjohnson]

Fix #19457.

This PR adds file format loads for CUBE and 3DL 3D Color LUT files (both of which can be exported from photoshop and other applications) as well as LUTPass for postprocessing and an associated example. The loaders generate both 2D and 3D data textures which LUTPass can use which means it supports both WebGL1 and 2.

The LUTs used in the demo are provided free from RocketStock.com which I've added an attribution for at the top of the example.

Here's the example page from this PR:

https://raw.githack.com/gkjohnson/three.js/lut-pass/examples/webgl_postprocessing_3dlut.html

And here's the demo I originally made in another repo that uses a photograph and quite a few other LUTs for demonstration:

https://gkjohnson.github.io/threejs-sandbox/3d-lut/

[gkjohnson]

When I generate a screenshot it all looks black 🤔 not sure why that is. Have I structured something wrong in the example for taking screenshots?

[mrdoob]

Beautiful! We should rename these to InstaFilterLoader 😁

[mrdoob]

Thanks!

[mrdoob]

When I generate a screenshot it all looks black 🤔 not sure why that is. Have I structured something wrong in the example for taking screenshots?

No idea...
I've just ran npm run make-screenshot webgl_postprocessing_3dlut locally and it generated a good screenshot 🤔