gltf-insight Khronos glTF "test" files

The repository glTF-Sample-Models host a number of "feature test" glTF files.

Ideal, all these files should be able to be opened by glTF-insight without failure. This issue will keep track of the current state of these tests.

State column should contains either ✔️ ❔ ❌

Conformance tests

Model name (w/ link)	State	Comment
Alpha Blend Mode Test	❌	It seems that the glTF tree isn't loaded correctly, like in #11 but not the same issue
Boom Box with Axes	✔️
Metal-Rough Spheres	✔️	PBR shader has been implemented like in the standard viewer
Morph-Primitives Test	✔️	(default weight are ommited by gltf-Insight. Moving weight with slider works)
MultiUV Test	❌	currently not supporting multiple texture coordinate sets. This may or may
Normal-Tangent Test	✔️
Normal-Tangent Mirror Test	❌	Supplied tangent in geometry needs to be used. 4th component of tangents in geometry data indicate right/left handedness
Orientation Test	❌	glTF scene tree loading issue like #11
Texture Coordinates Test	❔	Software does not load that model because an exception is thrown like in #10
Texture Settings Test	❔	Same problem as the above line
Vertex Color Test	✔️	We are not loading vertex colors.

Steps likely to increase standard conformance and pass these tests :

[x] fix flipped Y/green normal
[x] fix issue #11
[x] Support COLOR_0 vertex attribute
[ ] Support TEXCOORD_1vertex attribute (multiple uv sets)
[ ] fix issue #10
[ ] Selectively choose to use loaded and/or generate tangent when computing cotangent space in fragment shader (see Sasha Willem's configurable PBR shader. Pass a #define or uniform depending on data)