Forbid ClassVar and Final within TypedDict body

Author: InSyncWithFoo

docs/spec/typeddict.rst

@@ -508,6 +508,13 @@ make type declarations self-contained, and to simplify the
 implementation of type checkers.
 
 
+ClassVar and Final items
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+``ClassVar`` and ``Final`` are not allowed as qualifiers for an item
+of a ``TypedDict``. Such an item also causes a hard error at runtime.
+
+
 Backwards Compatibility
 ^^^^^^^^^^^^^^^^^^^^^^^