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

[Stefan Monnier]

> IIUC we allocate an array internally as well during the sorting phrase, but
> then we can't return it as-is or with a thin wrapper (if only because the
> user expects back a list, not a vector), so we'll need to allocate a whole
> new list to avoid mutating the original. And our GC is worse than JVM's.

When it matters, people can use `:in-place`.


        Stefan