Fix project_panel::NewSearchInDirectory to work on files (#23696)

Closes #23383

This PR changes `project_panel::NewSearchInDirectory` to open project
search filtered by the parent directory when triggered on a file, rather
than doing nothing.

Release Notes:

- Improved `project_panel::NewSearchInDirectory` to search the parent
directory when triggered on a file

crates/project_panel/src/project_panel.rs

@@ -2257,14 +2257,36 @@ impl ProjectPanel {
         cx: &mut Context<Self>,
     ) {
         if let Some((worktree, entry)) = self.selected_sub_entry(cx) {
-            if entry.is_dir() {
+            let dir_path = if entry.is_dir() {
+                entry.path.clone()
+            } else {
+                // entry is a file, use its parent directory
+                match entry.path.parent() {
+                    Some(parent) => Arc::from(parent),
+                    None => {
+                        // File at root, open search with empty filter
+                        self.workspace
+                            .update(cx, |workspace, cx| {
+                                search::ProjectSearchView::new_search_in_directory(
+                                    workspace,
+                                    Path::new(""),
+                                    window,
+                                    cx,
+                                );
+                            })
+                            .ok();
+                        return;
+                    }
+                }
+            };
+
             let include_root = self.project.read(cx).visible_worktrees(cx).count() > 1;
             let dir_path = if include_root {
                 let mut full_path = PathBuf::from(worktree.read(cx).root_name());
-                    full_path.push(&entry.path);
+                full_path.push(&dir_path);
                 Arc::from(full_path)
             } else {
-                    entry.path.clone()
+                dir_path
             };
 
             self.workspace
@@ -2276,7 +2298,6 @@ impl ProjectPanel {
                 .ok();
         }
     }
-    }
 
     fn move_entry(
         &mut self,