[GLTF] Reuse mesh buffer items

Multiple copies of the mesh data are included when with the same mesh is added to the scene multiple times. I would be nice to identify that the mesh data is already present and avoid adding it again. This will allow us to have smaller files and in some cases speed up write times.

Bellow is a simple example of a scene where we should try to have a single buffer item.

from trimesh import Scene
from trimesh.creation import box
from trimesh.transformations import translation_matrix
import trimesh

scene = Scene()
box_1 = box()
box_2 = box()
print(trimesh)

scene.add_geometry(box_1, 'box_1', transform=translation_matrix((1, 1, 1)))
scene.add_geometry(box_2, 'box_2', transform=translation_matrix((-1, -1, -1)))

scene.export('boxes2.glb')

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I may have a chance to tackle this myself, but wanted to capture this task here incase there were any upfront objections to adding this.

[mikedh]

Ah nevermind that just combines them into one big buffer. Dedupe branch here with the hashing strategy works for meshes: https://github.com/mikedh/trimesh/tree/gltf/dedupe

[mikedh]

Hmm, what about the existing merge_buffers option? IE scene.export(file_type='gltf', merge_buffers=True). It seems like it does pretty much this, maybe it should be selected by default?

# merge_buffers=False
len(acc): 7 len(buff): 7
# merge_buffers=True
len(acc): 7 len(buff): 1