typing.Reversible doesn't fully support the reversing protocol #170
Description
typing.Reversible doesn't work with types that are supported by reserved() but don't have the __reversed__ method. E.g. tuple, str, bytes, bytearray, and array.
>>> issubclass(tuple, typing.Reversible)
False
>>> issubclass(str, typing.Reversible)
False
>>> issubclass(bytes, typing.Reversible)
False
>>> issubclass(bytearray, typing.Reversible)
False
>>> issubclass(array.array, typing.Reversible)
False
The reversing protocol as well as the iterating protocol is supported not only by special method, but implicitly if the class has implemented __getitem__ and __len__ methods.
>>> class Counter(int):
... def __getitem__(s, i): return i
... def __len__(s): return s
...
>>> list(reversed(Counter(10)))
[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
>>> issubclass(Counter, typing.Reversible)
False