Reuse existing bundled file editors (#51053)

Closes #46837

Reuse the existing read-only bundled editor when opening default
settings or default key bindings again, instead of creating a duplicate
tab each time.

Also adds a regression test covering repeated `OpenDefaultSettings`
dispatches.

### Before


https://github.com/user-attachments/assets/ac2477b0-dc57-451c-a400-667c3613da2c


### After


https://github.com/user-attachments/assets/309fbd32-6dad-40a0-a864-b638a583ef52



Before you mark this PR as ready for review, make sure that you have:
- [x] Added a solid test coverage and/or screenshots from doing manual
testing
- [x] Done a self-review taking into account security and performance
aspects
- [x] Aligned any UI changes with the [UI
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)

Release Notes:

- Fixed default settings and default key bindings reopening duplicate
tabs instead of reusing the existing tab.

crates/zed/src/zed.rs

@@ -2008,13 +2008,29 @@ fn open_local_file(
 }
 
 fn open_bundled_file(
-    workspace: &Workspace,
+    workspace: &mut Workspace,
     text: Cow<'static, str>,
     title: &'static str,
     language: &'static str,
     window: &mut Window,
     cx: &mut Context<Workspace>,
 ) {
+    let existing = workspace.items_of_type::<Editor>(cx).find(|editor| {
+        editor.read_with(cx, |editor, cx| {
+            editor.read_only(cx)
+                && editor.title(cx).as_ref() == title
+                && editor
+                    .buffer()
+                    .read(cx)
+                    .as_singleton()
+                    .is_some_and(|buffer| buffer.read(cx).file().is_none())
+        })
+    });
+    if let Some(existing) = existing {
+        workspace.activate_item(&existing, true, true, window, cx);
+        return;
+    }
+
     let language = workspace.app_state().languages.language_for_name(language);
     cx.spawn_in(window, async move |workspace, cx| {
         let language = language.await.log_err();
@@ -4965,6 +4981,54 @@ mod tests {
         );
     }
 
+    #[gpui::test]
+    async fn test_bundled_files_reuse_existing_editor(cx: &mut TestAppContext) {
+        let app_state = init_test(cx);
+        cx.update(init);
+
+        let project = Project::test(app_state.fs.clone(), [], cx).await;
+        let _window = cx.add_window(|window, cx| MultiWorkspace::test_new(project, window, cx));
+
+        cx.update(|cx| {
+            cx.dispatch_action(&OpenDefaultSettings);
+        });
+        cx.run_until_parked();
+
+        let multi_workspace = cx.windows()[0].downcast::<MultiWorkspace>().unwrap();
+        let first_item_id = multi_workspace
+            .update(cx, |multi_workspace, _, cx| {
+                multi_workspace.workspace().update(cx, |workspace, cx| {
+                    workspace
+                        .active_item(cx)
+                        .expect("default settings should be open")
+                        .item_id()
+                })
+            })
+            .unwrap();
+
+        cx.update(|cx| {
+            cx.dispatch_action(&OpenDefaultSettings);
+        });
+        cx.run_until_parked();
+
+        let (second_item_id, item_count) = multi_workspace
+            .update(cx, |multi_workspace, _, cx| {
+                multi_workspace.workspace().update(cx, |workspace, cx| {
+                    let pane = workspace.active_pane().read(cx);
+                    (
+                        pane.active_item()
+                            .expect("default settings should still be open")
+                            .item_id(),
+                        pane.items_len(),
+                    )
+                })
+            })
+            .unwrap();
+
+        assert_eq!(first_item_id, second_item_id);
+        assert_eq!(item_count, 1);
+    }
+
     #[gpui::test]
     async fn test_bundled_languages(cx: &mut TestAppContext) {
         let fs = fs::FakeFs::new(cx.background_executor.clone());