Ensure align_family works well with VMobject fill

manimlib/mobject/types/vectorized_mobject.py

@@ -878,6 +878,12 @@ class VMobject(Mobject):
             mob.get_joint_products()
         return self
 
+    def invisible_copy(self):
+        result = self.copy()
+        result.append_vectorized_mobject(self.copy().reverse_points())
+        result.set_opacity(0)
+        return result
+
     def insert_n_curves(self, n: int, recurse: bool = True):
         for mob in self.get_family(recurse):
             if mob.get_num_curves() > 0:
@@ -1107,6 +1113,7 @@ class VMobject(Mobject):
             if refresh:
                 self.refresh_triangulation()
                 self.refresh_joint_products()
+            return self
         return wrapper
 
     @triggers_refreshed_triangulation