* lisp/sort.el (sort-on):
* doc/lispref/sequences.texi (Sequence Functions):
* etc/NEWS:
Remove the `sort-on` function which is now completely superseded by
the extended `sort` in features, ease of use, and performance.

* doc/lispref/help.texi (Accessing Documentation):
* doc/lispref/strings.texi (Text Comparison):
Use the new sort calling convention (bug#69709).

* doc/lispref/sequences.texi (Sequence Functions):
Update the manual about the new `sort` arguments.

* etc/NEWS: Announce the changes (bug#69709).

Postpone the creation of a new list to after sorting which turns out to
be a lot faster (1.1x - 1.5x speedup).

* src/fns.c (sort_list, sort_vector, Fsort):
Create the new list when moving the data out from the temporary array.

This gives a 1.5x-2x speed-up when using the default :lessp value,
by eliminating the Ffuncall overhead.

* src/sort.c (order_pred_lisp, order_pred_valuelt): New.
(merge_state, inorder, binarysort, count_run, gallop_left, gallop_right)
(merge_init, merge_lo, merge_hi, tim_sort):
* src/fns.c (Fsort):
When using value<, call it directly.

Add the :key, :lessp, :reverse and :in-place keyword arguments.
The old calling style remains available and is unchanged.

* src/fns.c (sort_list, sort_vector, Fsort):
* src/sort.c (tim_sort):
Add keyword arguments with associated new features.
All callers of Fsort adapted.
* test/src/fns-tests.el (fns-tests--shuffle-vector, fns-tests-sort-kw):
New test.

The original timsort code did provide for a key (accessor) function
along with the necessary storage management, but we dropped it because
our `sort` function didn't need it.

Now it's been put back since it seems that it will come in handy after all.

* src/fns.c (sort_list, sort_vector, Fsort): Pass Qnil as key function
to tim_sort.
* src/sort.c (reverse_slice, sortslice_copy)
(sortslice_copy_incr, sortslice_copy_decr, sortslice_memcpy)
(sortslice_memmove, sortslice_advance): New functions.
(sortslice): New type.
(struct stretch, struct reloc, merge_state)
(binarysort, merge_init, merge_markmem, cleanup_mem)
(merge_register_cleanup, merge_getmem, merge_lo, merge_hi, merge_at)
(found_new_run, reverse_sortslice, resolve_fun, tim_sort):
Merge back previously discarded parts from the upstreams timsort code
that dealt with key functions, and adapt them to fit in.

* doc/lispref/sequences.texi (Sequence Functions):
* doc/lispref/numbers.texi (Comparison of Numbers):
* doc/lispref/strings.texi (Text Comparison):
Document the new value< function.

* etc/NEWS: Announce.