Make Makie.mesh compatible with MultiMesh (GeometryBasics refactor)

[ffreyer]

Description

This is test/prototype for using MetaMesh from JuliaGeometry/GeometryBasics.jl#219 to render a mesh with materials loaded with JuliaIO/MeshIO.jl#98. This is effectively a continuation of #4319.

With this branch (and the related MeshIO, ShaderAbstractions & GeometryBasics branches), using https://free3d.com/3d-model/girl-blind-703979.html:

filepath = "path/to/14-girl-obj/girl OBJ.obj"
metamesh = load(filepath)

# Fix filename, convert white -> alpha
img = map(FileIO.load("path/to/14-girl-obj/tEXTURE/FACE Base Color apha.png")) do c
    Makie.RGBA{Makie.N0f8}(c.r, c.g, c.b, 1 - c.r)
end
metamesh[:materials]["FACE"]["diffuse map"]["image"] = img

# this splits up the mesh, extracts material parameters, loads the remaining textures and generates multiple mesh plots
f, a, p = Makie.mesh(metamesh)

Type of change

• New feature (non-breaking change which adds functionality)

Checklist

• Added an entry in CHANGELOG.md (for new features and breaking changes)
• Added or changed relevant sections in the documentation
• Added unit tests for new algorithms, conversion methods, etc.
• Added reference image tests for new plotting functions, recipes, visual options, etc.

[ffreyer]

I need to stop using rebase...

I added this as a refimg test:

 begin
    m = load(Makie.assetpath("sponza/sponza.obj"))
    f, a, p = mesh(m)
    cameracontrols(a).settings.center[] = false
    cameracontrols(a).settings.fixed_axis[] = false # irrelevant for test
    update_cam!(a.scene, Vec3f(-15, 7, 1), Vec3f(3, 5, 0), Vec3f(0,1,0))
    f
end

I think we can also use this as a example for further lighting improvements in the future, e.g. adding an ambient multiplier or adding normal maps, bump maps etc. The model is the Sponza model from https://casual-effects.com/data/, about 6MB in total, loosely licensed for non-commerical use.