Fix gamma (srgb EOTF) for GLTF via Asset3D embedded rgb(a) textures

[Wumpf]

What

Fix gltf loader assuming that the mesh shader doesn't apply the EOTF, when it fact it does (i.e. it calls linear_from_srgb)

Reference - via raw_mesh which was unaffected:

Before:

After:

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[emilk]

My bad!

[Wumpf]

OETF/EOTFing is hard!