[WIP] glTF asset loading

[ykafia]

PR Details

Implementation of a glTF asset loader for Stride using the SharpGLTF libraries.

Description

• Adding more IVertex C# struct definitions for the may different kind of mesh data
• Creating a parser from glTF to Stride
• Implementing the necessary Asset importer classes for glTF

Related Issue

#603

Motivation and Context

With FBX being a cumbersome proprietary file format and assimp not being complete, glTF imposed itself as a feature complete opensource 3D scene file specification, game engine friendly. Stride depends on Assimp to load glTF, but the current implementation doesn't handle glTF 2.0 which includes skinning and animations.

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My change requires a change to the documentation.
• I have added tests to cover my changes.
• All new and existing tests passed.

[CLAassistant]

All committers have signed the CLA.

[Eideren]

this.Equals(obj) recurses upon itself indefinitely afaik since obj is still of type object, use this instead:

public override bool Equals(object obj) => obj is VertexPositionNormalTextureSkinning vpnts && this.Equals(vpnts);

[xen2]

I assume this PR is still in progress (no gltf code yet) so I converted it to draft.

[ykafia]

Yes, but even though there will be gltf code i'd prefer to keep it as a draft as long as i haven't figured everything out. I'm taking a pause from the skinning part to invest my time on the importing side.