Refactor RefPathIndex initialization and attribute indexing

- Removed the `populate_initial_ref_path_index` method from `ChangeProcessor` and integrated its functionality into the `RefPathIndex` struct with a new `populate_from_dir` method.
- Updated the `ServeSession` to initialize `RefPathIndex` by populating it directly from the project root directory, ensuring pre-existing `Rojo_Ref_*` attributes are indexed correctly.
- This refactor enhances code organization and improves the efficiency of attribute indexing during session initialization.

src/serve_session.rs

@@ -174,7 +174,11 @@ impl ServeSession {
 
         let (tree_mutation_sender, tree_mutation_receiver) = crossbeam_channel::unbounded();
         let suppressed_paths = Arc::new(Mutex::new(std::collections::HashMap::new()));
-        let ref_path_index = Arc::new(Mutex::new(crate::RefPathIndex::new()));
+        let ref_path_index = {
+            let mut index = crate::RefPathIndex::new();
+            index.populate_from_dir(root_project.folder_location());
+            Arc::new(Mutex::new(index))
+        };
 
         let git_repo_root = crate::git::git_repo_root(root_project.folder_location());