* `Ord` inherits from `Eq`
* `TotalOrd` inherits from `TotalEq`
* `TotalOrd` inherits from `Ord`
* `TotalEq` inherits from `Eq`
This is a partial implementation of #12517.
very small runs.
This uses a lot of unsafe code for speed, otherwise we would be having
to sort by sorting lists of indices and then do a pile of swaps to put
everything in the correct place.
Fixes#9819.