bug#69709: `sort` interface improvement and universal ordering predicate

[Eli Zaretskii <eliz@gnu.org>]

> From: Mattias Engdegård <mattias.engdegard@gmail.com>
> Date: Sun, 10 Mar 2024 14:28:02 +0100
> 
> The proposed sorting function interface would be
> 
>   (new-sort seq &key key lessp destructive)

A nit: let's go with a name that doesn't have "new" as part of it.
Something like "lsort" or "xsort" or somesuch.  (I don't suggest
"nsort" because 'n' as the first character has a special meaning in
Emacs Lisp, so I'd like to avoid confusion.)

> because the keyword interface is easier to read and write than a lengthening list of optional positional parameters, and can be extended more gracefully. For example, it could be handy to have a `reversed` (or `descending`) parameter. The parsing cost is not significant.
> 
> Instead of inventing a new and rather meaningless function name, I suggest we re-use `sort` and allow both
> 
>   (sort seq lessp)                       ; old-style
>   (sort seq &key key lessp destructive)  ; new-style
> 
> since they are easy to distinguish, and let `destructive` default to false in new-style calls, true in the old style.

Do you intend to present an implementation that replaces sort-on as
well?

And what about performance?

Thanks.