fix: add a -s option to format a revision and its descendants `hg fix -r abc123` will format that commit but not its descendants. That seems expected given the option name (`-r`), but it's very rarely what the user wants to do. The problem is that any descendants of that commit will not be formatted, leaving them as orphans that are hard to evolve. They are hard to evolve because the new parent will have formatting changes that the orphan doesn't have. I talked to Danny Hooper (who wrote most of the fix extension) about the problem and we agreed that deprecating `-r` in favor of a new `-s` argument (mimicing rebase's `-s`) would be a good way of reducing the risk that users end up with these hard-to-evolve orphans. So that's what this patch implements. Differential Revision: https://phab.mercurial-scm.org/D8287