Restore blender addon to export quad gltf. about godot-subdiv

[fire]

I restored some old code.

https://github.com/fire/glTF-Blender-IO/tree/OMI_ngon_encoding WIP: Does not export quads yet.

Old one that works on Blender 2.79 https://github.com/fire/glTF-Blender-IO/tree/FB_ngon_encoding

[tefusion]

If its just quads I don't think an extra extension is necessary. Like, if it's not too much effort it'd be better than the current solution by a mile cause you could show the problematic faces, but in most cases the recreation by merging vertices should work (you have to actively try to break it, like disconnecting a face so vertices overlap)

[fire]

Because of the other pr of enabling loop subdivide for trimeshes, this has less importance.