Add a --edit flag

[MrJohz]

The --edit flag forces the editor to be shown, even if it would have been hidden due to the --no-edit flag or another flag that implies it (such as --message or --stdin).

This fixes #5379

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

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[arxanas]

In other contexts, --edit means "switch to the commit as the new working copy and start editing it", which is inconsistent with its usage here (and the current usage of --no-edit). Maybe it should be something like --editor/--no-editor?

[MrJohz]

That makes sense to me and I'm happy to make the change. To briefly play devil's advocate:

• That makes this a breaking change for anyone who's already using --no-edit in scripts etc
• Both Git and Mercurial use --edit (and --no-edit for Git) to invoke/avoid invoking the editor.

But internal consistency is more important than consistency with those other tools, so I'm happy to make the change if you/other people would prefer it that way.

[PhilipMetzger]

What about --open-editor as a flag? Also adhere to the commit style outlined here: https://github.com/jj-vcs/jj/blob/main/docs/contributing.md#code-reviews

[arxanas]

Looks good to me overall, thanks for implementing this! Also be sure to adjust the commit message as per @PhilipMetzger's comment.

Re --editor vs --no-editor, I also asked in this Discord message. It seems like there's many factors to consider, so let's not block this PR on that. I'll open a separate discussion.

[MrJohz]

What's the convention here for who merges, when that happens, etc? I think this is ready to go now. @arxanas

[PhilipMetzger]

The procedure currently is that Martin invites you to the jj-vcs/contributors team and then you can land it yourself.