godot-core: builtin: reimplement Rect2i to provide functionality on outer type

Author: yannick-was-taken

godot-core/src/builtin/mod.rs

@@ -330,6 +330,7 @@ macro_rules! real {
 /// The side of a [`Rect2`] or [`Rect2i`].
 ///
 /// _Godot equivalent: `@GlobalScope.Side`_
+#[derive(Copy, Clone)]
 #[repr(C)]
 pub enum RectSide {
     Left = 0,