Introduce the temporary/retained workspace behavior based on whether the sidebar is open (#53267)

Self-Review Checklist:

- [ ] 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
a018333d41Mikayla Maki committed on 4/6/2026, 9:42:04 PM· committed by GitHubparentbc4d25c
14 files changedLine totals unavailable