Add texture packing of masks

Basically how it would work is you can make a mask layer then when you make your packing presets you can select it or its corresponding channel

here is an example

for this model I want to mask the red so I can put a team color there instead

currently what I would have to do is mask a mask for the area (in this case I can use the red mask) and then I have to pack it into the texture externally

here is something the ui could look like this where there is something like 64 channels for masks (overkill but it's there if needed)

No files, tests, or entry points are named. Start by locating the packing-preset workflow and mask-layer/channel handling; done means a mask or its channel can be selected in a packing preset and packed into the texture without external processing.

Written by the indexing model from the issue text.