With this change a warning is shown if the user does not explicitly specify the target revision, but the behavior is unchanged (it still defaults to the working copy).
In the future the warning will be turned into an error. In other words, it will be required to specify target revision.
The bulk of the changes here are to prepare tests for the upcoming change, to make the transition easier.
For additional details please see:
* https://github.com/jj-vcs/jj/issues/5374
* https://github.com/jj-vcs/jj/discussions/5363
The problem is that author names are variable-length by nature, and format_*()
can be customized in that way. Commit ids are redundant in most cases where
commits aren't diverged.
We could add some format_short_fixed_length_*() hook points, but it would
probably be easier to just customize the annotation template at all.
