As part of #105779, the active status of UV maps won't be stored in
CustomData anymore, so it has to be retrieved from a higher level.
The best way to do that is to retrieve it once and pass around the BMesh
custom data offset as a "key" to the data. This should also decrease
function call overhead in this code (not that it was a bottleneck).
Pull Request: https://projects.blender.org/blender/blender/pulls/105904
21e3b4483f