git_ui: Git panel polish (#25164)

- Hides header when no active repo/no repo
- Entire commit editor now has i-beam cursor on hover
- Adds an icon to the project diff tab

Release Notes:

- N/A
086f002f44Nate Butler committed on 2/19/2025, 3:33:41 PM· committed by GitHubparentc0c48d3
2 files changedLine totals unavailable