`<[T]>::sort_by_index` and `<[T]>::sort_by_key_and_index`

Maybe some API may be composed in order to sort multiple slices with one leader? Structure of arrays basically.

First thing coming to mind is something like

let slice_a;
let slice_b;

slice_a.manual_sort_unstable(|slice, i, j| {
    mem::swap(&mut slice[i], &mut slice[j]);
    mem::swap(&mut slice_b[i], &mut slice_b[j]);
});