Add decorator

(cherry picked from commit 8e80555393)

game/scripts/cds.rpy

@@ -1,3 +1,27 @@
+python early hide:
+    import inspect
+    __register_params = frozenset(inspect.signature(renpy.register_statement).parameters).difference({"name", "parse"})
+    def register_decorator(cls):
+        """
+        A class decorator which registers a new statement.
+
+        The name of the statement will be the class name unless a `name` class attribute is present, which should be a string.
+
+        The `parse` method should be a static method that returns an object which will be passed to the other methods as `self`.
+        Returning an instance of the class is disabled for now.
+        """
+        # security
+        def raiser(*args, **kwargs):
+            raise NotImplementedError("Returning an instance of the class is disabled")
+        cls.__init__ = raiser
+
+        name = getattr(cls, "name", cls.__name__)
+        parse = getattr(cls, "parse", cls) # left in
+        renpy.register_statement(name,
+            parse=parse,
+            **{k:getattr(cls, k) for k in __register_params.intersection(vars(cls))})
+        return cls
+
 python early:
     def parse_chibi(l):
         who = l.simple_expression()