Emit a BreadcrumbsChanged event when associated settings changed (#36177)

Closes https://github.com/zed-industries/zed/issues/36149

Release Notes:

- Fixed a bug where changing the `toolbar.breadcrumbs` setting didn't
immediately update the UI when saving the `settings.json` file.

crates/editor/src/items.rs

@@ -1036,6 +1036,10 @@ impl Item for Editor {
                 f(ItemEvent::UpdateBreadcrumbs);
             }
 
+            EditorEvent::BreadcrumbsChanged => {
+                f(ItemEvent::UpdateBreadcrumbs);
+            }
+
             EditorEvent::DirtyChanged => {
                 f(ItemEvent::UpdateTab);
             }