Derive Ord and PartialOrd for ClassName type

This PR adds two simple derives (Ord and PartialOrd) to allow the storage of ClassName type in ordered maps (BTreeSet/BTreeMap etc.).

godot-core/src/meta/class_name.rs

@@ -96,7 +96,7 @@ impl ClassNameSource {
 /// This struct is very cheap to copy. The actual names are cached globally.
 ///
 /// If you need to create your own class name, use [`new_cached()`][Self::new_cached].
-#[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug)]
 pub struct ClassName {
     global_index: u16,
 }