Self-Review Checklist:

- [X] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [ ] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [ ] Tests cover the new/changed behavior
- [ ] Performance impact has been considered and is acceptable

Fix an issue introduced by PR #58237 where IME could not be enabled when
multiple windows were open.
The fix ensures that `update_ime_enabled` only updates IME state for the
active window.

Release Notes:

- N/A