WebGPURenderer: WebGL fallback, use shared UBOs for common uniform groups

[aardgoose]

Related issue: #29386

WebGL examples broken by lack of shared buffers now work.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	686.07 169.79	686.07 169.79	+0 B +0 B
WebGPU	832.49 223.05	832.51 223.04	+16 B -4 B
WebGPU Nodes	832 222.92	832.02 222.92	+16 B -4 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	462.42 111.53	462.42 111.53	+0 B +0 B
WebGPU	529.96 142.77	529.98 142.77	+16 B -4 B
WebGPU Nodes	486.62 132.63	486.64 132.63	+16 B -2 B

[sunag]

Great revision, thanks! This should also have a positive impact on performance.

/cc @RenaudRohlinger #29386 (comment)