Add Luau-style ref paths migration plan and update related tests

- Introduced a new migration plan for converting `Rojo_Ref_*` attribute paths to Luau require-by-string style, enhancing portability with relative paths.
- Updated existing test snapshots to reflect the new path formats, ensuring consistency across various scenarios.
- Enhanced the `compute_relative_ref_path` and `resolve_ref_path` functions to support the new path semantics, improving path resolution logic.
- Refactored related code in `change_processor`, `syncback`, and `snapshot` modules to accommodate the new reference path handling.

These changes improve the robustness and maintainability of reference path management in the project.

src/snapshot/patch_apply.rs

@@ -144,7 +144,7 @@ fn finalize_patch_application(context: PatchApplyContext, tree: &mut RojoTree) -
     let mut path_rewrites = Vec::new();
     for (id, map) in context.path_refs_to_rewrite {
         for (prop_name, path) in map {
-            if let Some(target) = tree.get_instance_by_path(&path) {
+            if let Some(target) = tree.resolve_ref_path(&path, id) {
                 log::debug!(
                     "Resolved path reference {} -> {} (path: {})",
                     prop_name,