Load standalone materials from GLTF

[CadsoftBrianW]

Feature request

Forum Link: https://forum.babylonjs.com/t/standalone-gltf-materials/5481/2

• Load standalone materials from a gltf file.

Example GLTF file:
{
“asset”: {
“generator”: “COLLADA2GLTF”,
“version”: “2.0”
},
“materials”: [
{
“pbrMetallicRoughness”: {
“baseColorFactor”: [
0.800000011920929,
0.0,
0.0,
1.0
],
“metallicFactor”: 0.0
},
“name”: “Red”
}
]
}

[JoshKlint]

FYI: According to the GLTF spec, a GLTF file may contain collections of materials or other items.

I have suggested that a "material" tag be added to the root scene structure, analogous to the "scene" value that specifies which scene is the "main" one:
KhronosGroup/glTF#1420

[Popov72]

Should we add a flag in the GLTF loader to force loading materials that are not used by meshes or should the loader always load all materials from the GLTF file unconditionally?

[Popov72]

So we decided with @sebavan to load materials only if a given flag is true and we will only create an instance of a material if not already used by a mesh of the GLTF file.