CustomData_bmesh_copy_data_exclude_by_type was excessively optimized.
It only worked if the ordering (by name) of the attributes in both
customdata sets were the same.
Note that a blender::Set is used (with 32 slots of static storage)
to keep track of uninitialized destination layers.
Alternatives include:
* Storing a bitflag in CustomDataLayer.flag
* Using a static bool vector instead.
I don't especially care how it's done, pick one.
Pull Request: https://projects.blender.org/blender/blender/pulls/108683
9175d9b7c2