Part of https://github.com/zed-industries/zed/issues/9461. Similar PRs:

- https://github.com/zed-industries/zed/pull/39683
- https://github.com/zed-industries/zed/pull/39801


## Release Notes:

- Added the ability to separately highlight control flow keywords for
Shell Scripts for users and theme authors via the `keyword.control`
syntax property.

## Screenshots

| **Before** | **After** |
|:--:|:--:|
| <img width="719" height="860" alt="image"
src="https://github.com/user-attachments/assets/1e509e7b-a197-4fb0-a5da-bd3669b6bcd6"
/> | <img width="718" height="855" alt="image"
src="https://github.com/user-attachments/assets/9c5e253d-bfd6-4fe7-9e30-95af1b260fdf"
/> |