Add __class_getitem__ to Mobject

Author: JasonGrace2282

manim/mobject/mobject.py

@@ -2979,6 +2979,8 @@ def set_z_index_by_z_Point3D(self) -> Self:
         self.set_z_index(z_coord)
         return self
 
+    def __class_getitem__(cls, item: type) -> str:
+        return f"{cls.__name__}[{item.__name__}]"
 
 class Group(Mobject, metaclass=ConvertToOpenGL):
     """Groups together multiple :class:`Mobjects <.Mobject>`.