Codesplit WebGL/WebGPU entrypoints

[CodyJasonBennett]

Related issue: #29156

Description

Emits a build where three/webgpu re-exports from core to avoid user configuration or duplication. Each entrypoint will no longer bundle a unique copy of three.js but share a single copy.

To prevent future issues with tree-shaking (#28670), I've code split the common core and code specific to a backend.

// src/Three.core.js -> build/three.core.js -> build/three.core.min.js
export { Vector3 } from './math/Vector3.js';

// window.__THREE__ check for duplication here

// src/Three.js -> build/three.module.js -> build/three.module.min.js -> build/three.cjs

export * from './Three.core.js';
export { WebGLRenderer } from './renderers/WebGLRenderer.js';

// src/Three.WebGPU.js -> build/three.webgpu.js -> build/three.webgpu.min.js

export * from './Three.core.js';
export { WebGPURenderer } from './renderers/webgpu/WebGPURenderer.js';

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	686.07 169.79	337.84 78.55	-348.23 kB -91.25 kB
WebGPU	832.49 223.05	488.13 133.64	-344.36 kB -89.41 kB
WebGPU Nodes	832 222.92	15.5 5.23	-816.5 kB -217.69 kB

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	462.42 111.53	462.51 111.26	+93 B -269 B
WebGPU	529.96 142.77	529.96 142.77	+0 B +0 B
WebGPU Nodes	486.62 132.63	529.96 142.78	+43.34 kB +10.14 kB

[CodyJasonBennett]

Undid this change, but three.webgpu.nodes.js is unused, and duplicate with WebGPU (missing only the recent BundleGroup export). CI still measures WebGL, WebGPU, WebGPU + Nodes. Maybe it can measure the common core instead?

[donmccurdy]

Minor thing, but I'm seeing some duplication of build artifacts when running npm run build locally:

> ls ./build

three.cjs                 three.module.js           three.webgpu.min.js
three.core.min2.js        three.module.min.js       three.webgpu.nodes.js
three.core2.js            three.webgpu.js           three.webgpu.nodes.min.js

That aside, I think this looks like a good approach! Shared 'core' that the WebGL and WebGPU entrypoints can use, and that doesn't need to be exposed as a separate public entrypoint to users.