git_panel: Add group by staging view option (#59884)

# Objective

- Add a view option for group by staging.

## Solution

- Add a new option for group_by under git_panel view options, with 2
sections "Staged" and "Unstaged", with buttons (+/-) to stage and
unstage

## Testing

- cargo check -p git_ui

## 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 adheres to Zed's UI standards
([UX/UI](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
and
[icon](https://github.com/zed-industries/zed/blob/main/crates/icons/README.md)
guidelines)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

## Showcase

<img width="1679" height="1140" alt="Screenshot 2026-06-25 at 2 09
44 PM"
src="https://github.com/user-attachments/assets/1b605cad-7792-4823-983c-ada41be25504"
/>


---

Release Notes:

- Added group by staging view option

---------

Co-authored-by: Christopher Biscardi <chris@christopherbiscardi.com>
65e1c5af25Sathwik Chirivelli committed on 7/11/2026, 1:36:18 PM· committed by GitHubparentbc99075
5 files changedLine totals unavailable