Similar to 4bcd59d644. This probably got worse recently with
the generic attribute refactors for `Mesh`, but the final performance is
probably much better than older versions too.
Timings extracting attributes from a 16 million vertex grid (seconds):
- Corner float attribute: 0.72 -> 0.19
- Face float attribute: 0.60 -> 0.07
- UV map: 3.18 -> 0.05
8d0920ec6d