Mesh Update for instancing

[matajoh]

Mesh update doesn't work when enable_instancing is used on a mesh.

[matajoh]

Some thoughts:

1. We obviously leave the instanced mesh alone
2. Positions can be quantized as they currently are.
3. The transform quaternions will need to be quantized

So a few takeaways are:

1. This will need its own method and throw an unsupported exception if an instanced mesh is passed to the current function (and vice versa)
2. I think we continue to share vertex colors from the base mesh across all update instances until specific use cases demand otherwise.
3. Not sure how quaternions will handle this form of compression/quantization. Will require analysis.