Implements T78397
Extends the functionality of pack islands operator to allow packing UVs
to either the closest or active UDIM tile.
This provides 2 new options for packing UVs :
- Closest UDIM: Selected UVs will be packed to the UDIM tile they were placed on. If not present on a valid UDIM tile, the UVs will be packed to the closest UDIM in UV space
- Active UDIM: Selected UVs will be packed to the active UDIM image tile In case, no image is present in the UV editor, then UVs will be packed to the tile on the UDIM grid where the 2D cursor is located.