Refine str.maketrans and str.translate (#1613)

str.translate requires a Mapping or Sequence (in essence, anything
with __getitem__), not a Dict.

str.maketrans in the one-argument form only converts character string
keys to their unicode ordinal, leaving any of the values untouched.
This mapping may use both integers or strings as keys at the same time.

str.maketrans in the multi-argument form returns a dict with any of the
values str, int or None, as recognized by str.translate.

stdlib/3/collections/__init__.pyi

@@ -159,10 +159,10 @@ class UserString(Sequence[str]):
     if sys.version_info >= (3, 5):
         @staticmethod
         @overload
-        def maketrans(x: Union[Dict[int, Any], Dict[str, Any]]) -> Dict[int, Any]: ...
+        def maketrans(x: Union[Dict[int, _T], Dict[str, _T], Dict[Union[str, int], _T]]) -> Dict[int, _T]: ...
         @staticmethod
         @overload
-        def maketrans(x: str, y: str, z: str = ...) -> Dict[int, Any]: ...
+        def maketrans(x: str, y: str, z: str = ...) -> Dict[int, Union[int, None]]: ...
     def partition(self, sep: str) -> Tuple[str, str, str]: ...
     def replace(self: _UserStringT, old: Union[str, UserString], new: Union[str, UserString], maxsplit: int = ...) -> _UserStringT: ...
     def rfind(self, sub: Union[str, UserString], start: int = ..., end: int = ...) -> int: ...