Fix SOGS rendering scenes with SH 1 or 2

[vincentwoo]

SOGS scenes with SH 1 or 2 do not render currently, owing to missing handlers for their spherical harmonics.

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[willeastcott]

Thanks for the PR, @vincentwoo! Would you be able to pop a PR description up too please? Thanks! 🙏

[Copilot]

Pull Request Overview

This PR fixes rendering issues with SOGS scenes by introducing overloaded versions of the readSHData function to handle different spherical harmonics (SH) vector depths.

• Added a comment clarifying the function overload rationale.
• Introduced two new overloads of readSHData for SH vector sizes of 8 and 3.

[mvaligursky]

We'll need to fix WGSL shaders to match as well

[Copilot]

Pull Request Overview

This PR fixes the issue with SOGS scenes not rendering for SH 1 or 2 by adding missing shader handlers and updating the spherical harmonics coefficient calculations.

• Added new WGSL shader chunks for SOGS (gsplatSogsColorVS, gsplatSogsDataVS, and gsplatSogsSHVS)
• Updated shader code in both WGSL and GLSL to use the configurable SH_COEFFS macro instead of hard-coded values, and refined uniform usage
• Revised preprocessor conditionals in the common shader files to correctly include the appropriate shader chunks based on SH_BANDS

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/scene/shader-lib/wgsl/collections/shader-chunks-wgsl.js	Added imports and array entries for new SOGS shader chunks.
src/scene/shader-lib/wgsl/chunks/gsplat/vert/gsplatSogsSH.js	Updated SH coefficient reading logic to use SH_COEFFS and refined uniform references.
src/scene/shader-lib/wgsl/chunks/gsplat/vert/gsplatSogsData.js	Adjusted uniform references in data extraction functions.
src/scene/shader-lib/wgsl/chunks/gsplat/vert/gsplatSogsColor.js	Updated uniform usage in the color extraction function.
src/scene/shader-lib/wgsl/chunks/gsplat/vert/gsplatCommon.js	Reorganized SH_COEFFS macros and conditional includes based on SH_BANDS.
src/scene/shader-lib/glsl/chunks/gsplat/vert/gsplatSogsSH.js	Applied similar SH_COEFFS logic for reading coefficients in GLSL.
src/scene/shader-lib/glsl/chunks/gsplat/vert/gsplatCommon.js	Revised preprocessor definitions and conditional includes for proper SH handling in GLSL.

[slimbuck]

I've also updated the wgsl shaders to work with SOGS.