USDZLoader: Load metallic, roughness, emissive, occlusion textures and fix color spaces

[hybridherbst]

Related issues:

• USDZ Loader - Feature mismatch with USDZExporter #26616
• USDZLoader: Distinguish between text (supported) and binary (not supported) usd files and fix UV parsing #26709

Description

This PR adds USDZLoader support for metallic, roughness, emissive and occlusion textures in the respective correct color spaces. This is especially useful for files exported with USDZExporter.

With the PR, DamagedHelmet does roundtrip pretty nicely:

.glb	.usdz exported with USDZExporter and loaded with USDZLoader)

Thanks to @GitHubDragonFly for starting with #26623. This PR improves on it especially in terms of color spaces.

This PR does not fix a number of other issues with material roundtrip, notably

• texture scale and bias (which are the USD equivalent of specifying both "metalness" and "metalnessMap" and so on)
  • also affects normalStrength, occlusionScale and so on
• texture transforms
• clearcoat / clearcoatRoughness / ior (can be a future PR)

This contribution is funded by Needle

[mrdoob]

Nice!

[mrdoob]

Is there anything left from #26623?