Improve project search design details (#22529)

Closes https://github.com/zed-industries/zed/issues/22469 — and, aside
from fixing that issue also took the opportunity to make the
`file_search` icon dimensions feel better in comparison the other icons
in the Project Search area.

Release Notes:

- N/A

crates/search/src/project_search.rs

@@ -1905,6 +1905,7 @@ impl Render for ProjectSearchBar {
         }
 
         v_flex()
+            .py(px(1.0))
             .key_context(key_context)
             .on_action(cx.listener(|this, _: &ToggleFocus, cx| this.move_focus_to_results(cx)))
             .on_action(cx.listener(|this, _: &ToggleFilters, cx| {