GLTFSerializer New Extensions' Support

[thomlucc]

Update Babylon GLTF Serializer to support more glTF features and extensions.
Some extensions such Draco, need several step to beeing completed.

Milestones:

• EXT_mesh_gpu_instancing
• Draco Compression feature : add the support of Draco compression to Babylon. (PR)
• KHR_draco_mesh_compression : thanks to the previous support of Draco, add the extension to the GLTF serializer.

[thomlucc]

Thanks for the update @pandaGaume

[myfreeer]

Also consider:

• KHR_mesh_quantization: https://forum.babylonjs.com/t/keep-index-and-khr-mesh-quantization-attributes-on-glb-export/36782
• original image

[github-actions]

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