This PR improves the display of diff hunks:
- Deleted hunks now show a regular line indicator in the gutter when
expanded
- The rounding on the diff indicators in the gutter has been removed.
We also did some refactoring to ensure the sizing of the diff indicators
in the gutter were consistent.
#### Collapsed
<img width="1624" alt="Screenshot 2024-09-24 at 11 13 26 AM"
src="https://github.com/user-attachments/assets/f864dc83-cbbc-4d81-a62b-65c406ed310a">
#### Expanded
<img width="1624" alt="Screenshot 2024-09-24 at 11 13 35 AM"
src="https://github.com/user-attachments/assets/04d382ca-e0e6-4f1c-92eb-cd1e3a031c2c">
Release Notes:
- Improved the appearance of diff hunks in the editor.
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Co-authored-by: Max <max@zed.dev>