Closes #22447

When navigate forward/back, the focus moves from the ProjectSearchView's
result editor to the Pane, and then move to the ProjectSearchView, but
the event `on_focus_in` not triggered for ProjectSearchView, causing the
result editor to lose focus eventually.


https://github.com/zed-industries/zed/blob/f6dabadaf79bd29c89c8d55a1e9f1d33236f736e/crates/workspace/src/workspace.rs#L1372


https://github.com/zed-industries/zed/blob/f6dabadaf79bd29c89c8d55a1e9f1d33236f736e/crates/workspace/src/workspace.rs#L1385

Considering that the navigation might be triggered again in the next
frame, so use `on_next_frame` in `on_focus` event to move focus to
result editor.

Next frame:
- the blur event triggered for result editor.
- focus move from ProjectSearchView to result editor in `on_focus` event
for ProjectSearchView
- navigate again, focus moves from result editor to Pane then move back
to ProjectSearchView
- the focus not change during this frame, so no focus event happened for
ProjectSearchView.

![fix lost
focus1229](https://github.com/user-attachments/assets/bfaac839-7bcf-40e7-b3b4-1423d0510594)

Release Notes:

- Fix lost focus when navigate back in project search result

Co-authored-by: Kirill Bulatov <kirill@zed.dev>