git_graph: Wire up Vim mode navigation (#53609)
Added Vim mode navigation (`j`, `k`, `gg`, `G`) to the Git Graph view.
[gitgraph-vim.webm](https://github.com/user-attachments/assets/b2dd31a5-deb0-48ab-a48d-8721ee500dad)
Self-Review Checklist:
- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable
Closes #53525
Release Notes:
- Added vim mode navigation to git graph
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Co-authored-by: Anthony Eid <anthony@zed.dev>
