4309c32be6
Replace `BKE_mesh_face_flip_ex()` with `bke::mesh_flip_faces()`.
This gives better performance since it avoids custom data name
lookups for every face index, and processes data in a more cache
friendly way. Also remove the `CustomData_swap` API function
as mentioned in 09b6eac5c4.
Flipping 16 million faces, I observed a 3.25x speedup, from 760 to 230 ms.
Pull Request: https://projects.blender.org/blender/blender/pulls/110702