Objective

• This PR fixes the captured focus in modals.
• Fixes #63480 (and actually this was not specific to the task modal. it
  was generic and applied to all modals)

Solution

• Previously when a modal was opened the previous_focus_handle was
  stealing the focus because it was captured in show_modal. The fix was
  to capture it before calling show_modal or reveal_stashed_modal and
  pass it to show_modal. That fixes the bug :) (yuhuu).

Testing

• Tested by running the build and trying to reproduce the bug. I
  couldn't reproduce it anymore.
• For testing, a reviewer also needs to test the revelal stashed modal
  functionality. I did it with the file finder.

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content adheres to Zed's UI standards
  (UX/UI
  and
  icon
  guidelines)
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Release Notes:

• Fixed previous window focus handle not being captured correctly when
  opening modals