sort: add gen_sort_variants support for x/exp/slices
Also add a go:generate command to the standard library slices package.
For #61374
Change-Id: I7aae8e451b7c6c4390e0344257478d1a96a14189
Reviewed-on: https://go-review.googlesource.com/c/go/+/511660
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Eli Bendersky <eliben@google.com> Reviewed-by: Ian Lance Taylor <iant@google.com>