Reuse existing language servers for invisible worktrees (#30707)

Closes https://github.com/zed-industries/zed/issues/20767

Before:


https://github.com/user-attachments/assets/6438eb26-796a-4586-9b20-f49d9a133624


After:



https://github.com/user-attachments/assets/b3fc2f8b-2873-443f-8d80-ab4a35cf0c09



Release Notes:

- Fixed external files spawning extra language servers

crates/workspace/src/pane.rs

@@ -712,7 +712,7 @@ impl Pane {
         !self.nav_history.0.lock().forward_stack.is_empty()
     }
 
-    fn navigate_backward(&mut self, window: &mut Window, cx: &mut Context<Self>) {
+    pub fn navigate_backward(&mut self, window: &mut Window, cx: &mut Context<Self>) {
         if let Some(workspace) = self.workspace.upgrade() {
             let pane = cx.entity().downgrade();
             window.defer(cx, move |window, cx| {