revset: add working_copies() function

[ckoehler]

It includes the working copy commit of every workspace of the repo.

Implements #3384

Checklist

If applicable:

• I have updated CHANGELOG.md
• I have updated the documentation (README.md, docs/, demos/)
• I have updated the config schema (cli/src/config-schema.json)
• I have added tests to cover my changes

[ckoehler]

Not sure how to test this, would appreciate some pointers. Is there an easy way to create a repo with two workspaces, create some commits, and then compare those to the output of working_copies()? Sounds involved.

Nevermind, this looks straightforward: https://github.com/martinvonz/jj/blob/main/lib/tests/test_revset.rs#L332

[martinvonz]

Not sure how to test this, would appreciate some pointers. Is there an easy way to create a repo with two workspaces, create some commits, and then compare those to the output of working_copies()? Sounds involved.

Maybe it can be done similar to how we do it for @ here: https://github.com/martinvonz/jj/blob/7b3f8e8cb6cc33e5f183052822e081160bba564f/lib/tests/test_revset.rs#L331-L372

[yuja]

thanks.