cc @SomeoneToIgnore

## Summary

Follow-up to [this
discussion](https://github.com/zed-industries/zed/discussions/55352#discussioncomment-16919854).
This extracts the edit prediction and clipboard code from `editor.rs`
into `edit_prediction.rs` and `clipboard.rs`.

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