WebGLRenderer: Add support for packed normal maps.

[castano]

Previous PRs added support for packed RG normal maps to the WebGPU backend:

#31695
#32308

This PR extends that support to the WebGL backend by adding a packedNormalMap parameter to the fragment shader. This defines USE_PACKED_NORMALMAP and adds the necessary shader code to normal_fragment_maps. The parameter is set when the format of the textures bound to the normal map type is one of the packed format types (RGFormat, RG11_EAC_Format, or RED_GREEN_RGTC2_Format).

This also updates an incorrect webgl test, which used packed normal maps and did not shade them correctly due to the missing normal reconstruction code.

This contribution is funded by Ludicon

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	359.17 85.24	359.48 85.34	+311 B +98 B
WebGPU	626.44 174.13	626.44 174.13	+0 B +0 B
WebGPU Nodes	625.02 173.88	625.02 173.88	+0 B +0 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	490.91 119.65	491.22 119.74	+310 B +87 B
WebGPU	700.07 189.13	700.07 189.13	+0 B +0 B
WebGPU Nodes	649.27 176.49	649.27 176.49	+0 B +0 B

[castano]

@Mugen87 I think the CI error is unrelated to this change. Let me know if you think that's not the case and I'll investigate.

[Mugen87]

A rerun solved the CI issue 🎉 .

I'm okay with this change but I would like to hear the feedback of @donmccurdy because he was involved in the initial discussion.

@donmccurdy Are you okay with supporting packed normal maps like proposed in WebGLRenderer?

[Mugen87]

Oh wait, I see now he has given a heart to the PR. In this case, I assume he is fine with the change 😅 .

[Mugen87]

This PR extends that support to the WebGL backend

BTW: You have changed WebGLRenderer with this PR, not the WebGL backend of WebGPURenderer. That is located in src/rendereres/webgl-fallback.

The WebGL backend of WebGPURenderer already supports packed normals.

[donmccurdy]

Looks good to me, yes — thanks @castano and @Mugen87!