GLTFInstantiator mutates input data

[Pessimistress]

Actual Result

GLTFInstantiator.instantiate adds _node and _mesh fields to node and mesh:

luma.gl/modules/experimental/src/gltf/gltf-instantiator.js

Line 60 in c2f0534

if (!gltfNode._node) {

luma.gl/modules/experimental/src/gltf/gltf-instantiator.js

Lines 99 to 100 in c2f0534

	// TODO: avoid changing the gltf
	if (!gltfMesh._mesh) {

This prevents the gltf object from being used to create another instance, and there is no easy way to undo this change.

Expected Result

Input object should not be mutated.

Reproduce Steps

visgl/deck.gl#7950

To Do List

• Add label and assign to milestone
• Coding
• Test

[ibgreen]

I suppose a quick fix for 8.5 would be to deep clone everything (except arraybuffers) before instantiating.

That is probabely appropriate since for 9.0 the gltf instantiation needs to be refactored quite extensively.