This paves the way for the semantics of `jj undo` and `jj op revert` to
evolve independently. `jj op revert` is going to stay the low-level
command to apply the inverse of any operation. The new name is
consistent with `jj revert`, which applies the inverse of a commit.
`jj undo` on the other hand is planned to become a higher-level command,
which is more similar to, say, Ctrl+Z in typical GUI applications.
Running `jj undo` repeatedly will revert progressively older operations,
allowing the user to walk backwards in time. At the same time, `jj undo`
will lose the abilitly to revert arbitrary operations, to keep its
semantics simple and intuitive.
Related feature request "jj undo ergonomics":
https://github.com/jj-vcs/jj/issues/3700