WebGPURenderer: hardware clipping support.

[aardgoose]

Use WebGL 'WEBGL_clip_cull_distance' and WebGPU 'clip-distances' extensions if available for clipping where possible (not using intersections or alphaToCoverage and max 8 clipping planes).

Tested with WebGL, (WebGPU support not available to test).

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	692.21 171.45	692.21 171.45	+0 B +0 B
WebGPU	821.89 221.91	823.65 222.43	+1.76 kB +520 B
WebGPU Nodes	821 221.7	822.77 222.23	+1.76 kB +531 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	464.56 112.27	464.56 112.27	+0 B +0 B
WebGPU	542.09 146.75	543.86 147.32	+1.76 kB +561 B
WebGPU Nodes	498.03 136.5	499.8 137.03	+1.76 kB +528 B

[aardgoose]

@sunag @Mugen87

This now supports clip distances with WebGL and WebGPU, tested with Chrome 131 Beta which supports the clip-distance extension.

The addition of the declaration of gl_ClippingDistance[ n ] is crude, but I don't see other uses of builtins in WebGL.