Do not derive symbol highlights if they do not fit into multi buffer (#50948)

Release Notes:

- N/A

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/multi_buffer/src/multi_buffer_tests.rs

@@ -1285,7 +1285,7 @@ fn test_resolving_anchors_after_replacing_their_excerpts(cx: &mut App) {
         let mut ids = multibuffer
             .excerpts_for_buffer(buffer_2.read(cx).remote_id(), cx)
             .into_iter()
-            .map(|(id, _)| id);
+            .map(|(id, _, _)| id);
         (ids.next().unwrap(), ids.next().unwrap())
     });
     let snapshot_2 = multibuffer.read(cx).snapshot(cx);