Fix some issues with branch buffers (#18945)

* `Open Excerpts` command always opens the locations in the base buffer
* LSP features like document-highlights, go-to-def, and inlay hints work
correctly in branch buffers
* Other LSP features like completions, code actions, and rename are
disabled in branch buffers

Release Notes:

- N/A

crates/project/src/project_tests.rs

@@ -3892,7 +3892,7 @@ async fn test_rename(cx: &mut gpui::TestAppContext) {
     assert_eq!(range, 6..9);
 
     let response = project.update(cx, |project, cx| {
-        project.perform_rename(buffer.clone(), 7, "THREE".to_string(), true, cx)
+        project.perform_rename(buffer.clone(), 7, "THREE".to_string(), cx)
     });
     fake_server
         .handle_request::<lsp::request::Rename, _, _>(|params, _| async move {