Add missing definitions to Python 3 'traceback'

stdlib/3/traceback.pyi

@@ -6,5 +6,8 @@ import typing
 def format_exception_only(etype, value): ...
 def format_tb(traceback): ...
 def print_exc(limit=..., file=..., chain=...): ...
+def extract_stack(f=..., limit=...): ...
+def extract_tb(traceback, limit=...): ...
+def format_list(list): ...
 
 # TODO add more