Addons: Port of CSM to WebGPURenderer/Nodes

[aardgoose]

Related issue: #29295

Mostly working, the shader isn't rebuilt when switching between fade/non-fade modes without going via no shadow at the moment.

Uses a small addition to DirectionalLightNode to allow a lighting model to be intercepted and provide access to before and after shadow application light properties etc.

A hack is required in AnalyticLightNode to force the setting of the WorldNormal variable outside an 'if' clause.

There are artifact issues which I suspect are the result of using a lower precision depth map than the WebGLRenderer shadow map. Also if the floor casts shadows, it self shadows.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	687.15 170.18	687.15 170.18	+0 B +0 B
WebGPU	805.48 216.82	805.57 216.85	+91 B +28 B
WebGPU Nodes	804.99 216.68	805.08 216.71	+91 B +28 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	462.85 111.79	462.85 111.79	+0 B +0 B
WebGPU	535.29 144.41	535.38 144.44	+91 B +28 B
WebGPU Nodes	491.46 134.24	491.55 134.2	+91 B -35 B

[sunag]

The PR is great, but I think we need to think of a solution other than create new lights to get cascades shadows, I think it's a good opportunity to solve the WebGL hacks here.

Perhaps we can think of a class-oriented shadow partitioning system, so that the API is more similar to:

renderer.shadowMap.partitionNode = new CSMNode();

I think fade effect can be implemented for non-cascades shadows too, we have a port for that here.

three.js/src/nodes/lighting/AnalyticLightNode.js

Line 377 in cf28ac5

this.shadowColorNode = shadowColorNode = this.colorNode.mul( mix( 1, shadowNode.rgb.mix( shadowColor, 1 ), shadowIntensity.mul( shadowColor.a ) ) );

Maybe we could start by implementing the fade in another PR, and then the partitioning system in another?

[Mugen87]

Closing in favor of #29610.