Simplify remote workspace folder calculation for Dev Containers (#53829)

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 #53635 

Release Notes:

- Fixed issues with Windows pathing when calculating target workspace
directory for dev containers
5e6e41155eKyleBarton committed on 4/16/2026, 6:50:08 PM· committed by GitHubparentbb660d2
4 files changedLine totals unavailable