Add dev builds to speed up dev iteration

[ycw]

fix: #30829

Description

Idea #30851 (comment) is that creating stub build files to speed up dev iteration, and no bundling at all, e.g. content of build/three.module.js is now:

// dev mode
export * from '../src/Three.js';

This way build time is negligible, and /src can be reflected in devtools. Header comments is added to build files, so that the existent of /build is more reasonable upon debugging. Since dev phase and preview phase are now split, I added two npm scripts for verifying real build files.

In dev phase, users should run npm run dev or npm run dev-ssl

In preview phase, users should run npm run preview or npm run preview-ssl

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	336.44 78.37	336.44 78.37	+0 B +0 B
WebGPU	541.67 150.04	541.67 150.04	+0 B +0 B
WebGPU Nodes	541.14 149.93	541.14 149.93	+0 B +0 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	465.37 112.21	465.37 112.21	+0 B +0 B
WebGPU	614.51 166.09	614.51 166.09	+0 B +0 B
WebGPU Nodes	569.5 155.49	569.5 155.49	+0 B +0 B

[gkjohnson]

cc @Mugen87 @mrdoob @donmccurdy what do you think of a solution like this? I'm not sure if we need a "preview" script but this kind of solution would fix the recent issues associated with dev build times.