Refactor to isolate alacritty types into the terminal crate and offers
comparable apis where needed for similar functionality. However, these
are Zed-owned types instead of the dependency leaking across multiple
crates, making alacritty an implementation detail of the terminal crate.

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

Release Notes:

- N/A