std::min and std::max should require `TotalOrd`

[thestinger]

These do not handle partial orderings correctly. #12509 adds correct min and max methods to the Float trait to be used in place of these. These will likely end up as LLVM intrinsics at some point in the future too.

This can be fixed either by making the functions require TotalOrd, or by making them default methods on Ord and doing an override for floating point types.

[pongad]

Having methods min and max on integers and floating point seems to broad. I like changing to TotalOrd better. Can work on it if we have enough people agreeing with the change.

[thestinger]

There are now min and max methods on the Float trait. I don't really like the idea of reserving these method names, and I guess it's not actually going to work properly with deriving...

If they're going to be switched to TotalOrd, it should be done after the trait inheritance lands.

[pongad]

+1 to that plan.