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 ##42292

The text inserted in the search ('\$SEARCH') and replace ('$$OTHER')
inputs of the top-panel is a little anti-aesthetic, but that seems out
of scope for this issue.

Release Notes:

- '$' in the second clause of vim-style '%s/find/replace/g' actions is
correctly escaped.

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>