many containers implement Ord incorrectly

[thestinger]

They assume total ordering semantics are implemented by the underlying types.

We need to clarify the semantics that are desired from lexicographic ordering in the first place, and implement this consistently/correctly.

Test cases are needed to prevent regressions in these implementations too.

[huonw]

I assume that this would be fixed by implementing < in terms of < and <= in terms of <= etc, rather than implementing only one and using the default methods for the others.

[bluss]

I'm doing some work on this. It also includes tuples.

[emberian]

This seems to have been fixed in #8400. @blake2-ppc and @thestinger, can you confirm?

[huonw]

This is now done, thanks @bluss; and with the advent of partial_cmp and the iterator functions defined in #8400 it's now easier to be correct than incorrect, which is nice. (I also checked everything in collections.)