This is the natural counterpart of `jj undo`. Adding `jj redo` closes
the last gap in functionality to the "undo" features of typical GUI
applications. This is much more intuitive to new users and useful than
the previous undo semantics. (Which are preserved as `jj op revert`.)
Related feature request "jj undo ergonomics":
https://github.com/jj-vcs/jj/issues/3700
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