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.

[RenaudRohlinger]

This PR is a huge improvement. I’ve never relied on the current build outputs during development and always end up manually rewriting imports to point to src/.
I’ve noticed I’m not alone, many of Sunag’s PRs also include ../../src paths in the examples, which suggests a similar workflow.

Having this streamlined setup will make iteration smoother for everyone.

[gkjohnson]

Agreed - I think this should be merged. There have been a lot of reasons provided for why this is a valuable improvement and not a lot provided for why it's harmful to the dev process. To me it's clear from using the current dev workflow and from how other maintainers are modifying files for development that the current build time is only a drag on the current dev process.

[Mugen87]

Okay, I'm convinced. If multiple collaborators want this change because it improves their workflows, I don't want to be the one who blocks it 😅 .