git_graph: Hide commits that jj considers hidden

[timvermeulen]

Not sure if this is something the team is interested in right now given the current lack of jj-specific features, but I'm opening this anyway because the git graph is the main git feature in Zed that isn't very usable currently in git-colocated jj repos. Jujutsu creates a lot of "hidden" commits that don't show up in the jj log output, but they do currently show up in the git graph in Zed 🙂

This is a simple proof of concept that uses the jj binary to obtain the visible_heads() revset to pass to git log. We'll probably want to use jj-lib for proper jj support (though I don't know how feature complete it currently is).

I went with the visible_heads() revset because it most closely matches the current git log --all output, but we could also use the revsets.log config value (wrapped in heads(...)) to more closely match the output of jj log. Or we could add a Zed setting for this.

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Release Notes:

• Improved the git graph to hide commits that jj considers hidden.