Add ability to remove EXT_GPU_INSTANCING usage

[gkjohnson]

Is your feature request related to a problem? Please describe.

Right now you can convert a model to use EXT_GPU_INSTANCING instances using the instance command but this is not supported by a lot of engines (Unreal, other tools). It would be nice if it were possible to remove the extension usage in cases where you don't want it / can't use it.

Describe the solution you'd like

• Add a "--remove-instances" option to the "gltf-transform instance" command
• Or unpack instances and recompute them based on the settings of the instance command. Ie running a model that already has instances with the following command would remove all instances:

gltf-transform input.glb output.glb --min 10000000

Describe alternatives you've considered

Reading into the three.js editor and unpacking all instances manually.

Additional context

None

[donmccurdy]

I like the idea! This would involve:

• add an uninstance() (deinstance?) transform to the /functions package
• add a new command or flag to the CLI

I'm not immediately able to work on this, but PRs would be welcome.