Port the channel packer tool
Describe the problem
The Channel Packer tool found in MRTKv2 is useful for packing textures when access to other tools, like Photoshop, is not available.
Describe the solution you'd like
Move the Channel Packer: Channel Packer Editor + Other Shader Features by Cameron-Micka · Pull Request #3382 · microsoft/MixedRealityToolkit-Unity (github.com) from MRTK v2 to Graphics Tools.
Describe alternatives you've considered
Just use other image authoring tools like Photoshop or Gimp.
Additional context
Related issue: https://github.com/microsoft/MixedRealityToolkit-Unity/issues/8079
It would be good to redesign this UX so that it is more user friendly:

@Species521 do you have any ideas for how to improve this UX?
Re-opening since there is still work to re-design the UI and add docs.