The OSL image compilation step needed to be taught about the new UVTILE
format for UDIM textures.
A small missing feature from OIIO[1] means this is a bit uglier than it
needs to be. Once we update to a version of OIIO with the fix we can
remove the string replace part.
[1] 35cb6a83e2
Differential Revision: https://developer.blender.org/D13912
46ae083113