Add OrderedDict to typing_extensions (#5345)

stdlib/typing_extensions.pyi

@@ -22,6 +22,7 @@ from typing import (
     TypeVar,
     Union,
     ValuesView,
+    _Alias,
     overload as overload,
 )
 
@@ -68,6 +69,8 @@ class _TypedDict(Mapping[str, object], metaclass=abc.ABCMeta):
 # TypedDict is a (non-subscriptable) special form.
 TypedDict: object = ...
 
+OrderedDict = _Alias()
+
 if sys.version_info >= (3, 3):
     from typing import ChainMap as ChainMap