Blender Git Loki

Cleanup: isolate UDIM parameters into a struct

Passing multiple UDIM arguments into the packing function
is awkward especially since the caller may not be using UDIM.

Use an argument to store UDIM packing parameters which can be NULL,
which operates without any UDIM support.

Add a function that extracts these parameters out of the image space
allowing for multiple functions to take UDIM parameters in the future.