Fixed #30876 -- Moved classproperty() decorator to the django.utils.functional.

django/utils/functional.py

@@ -49,6 +49,18 @@ class cached_property:
         return res
 
 
+class classproperty:
+    def __init__(self, method=None):
+        self.fget = method
+
+    def __get__(self, instance, cls=None):
+        return self.fget(cls)
+
+    def getter(self, method):
+        self.fget = method
+        return self
+
+
 class Promise:
     """
     Base class for the proxy class created in the closure of the lazy function.