Add TypeGuard (PEP 647 draft) (#4879)

Author: gvanrossum

stdlib/3/typing.pyi

@@ -61,6 +61,7 @@ if sys.version_info >= (3, 10):
         def __init__(self, name: str) -> None: ...
     Concatenate: _SpecialForm = ...
     TypeAlias: _SpecialForm = ...
+    TypeGuard: _SpecialForm = ...
 
 # Return type that indicates a function does not return.
 # This type is equivalent to the None type, but the no-op Union is necessary to

third_party/2and3/typing_extensions.pyi

@@ -112,3 +112,6 @@ else:
         __name__: str
         def __init__(self, name: str) -> None: ...
     Concatenate: _SpecialForm = ...
+
+# PEP 647
+TypeGuard: _SpecialForm = ...