Add Protocols for mapping inside dictionary view objects (#14574)

stdlib/_typeshed/__init__.pyi

@@ -3,7 +3,7 @@
 # See the README.md file in this directory for more information.
 
 import sys
-from collections.abc import Awaitable, Callable, Iterable, Sequence, Set as AbstractSet, Sized
+from collections.abc import Awaitable, Callable, Iterable, Iterator, Sequence, Set as AbstractSet, Sized
 from dataclasses import Field
 from os import PathLike
 from types import FrameType, TracebackType
@@ -275,6 +275,16 @@ class SupportsWrite(Protocol[_T_contra]):
 class SupportsFlush(Protocol):
     def flush(self) -> object: ...
 
+# Suitable for dictionary view objects
+class Viewable(Protocol[_T_co]):
+    def __len__(self) -> int: ...
+    def __iter__(self) -> Iterator[_T_co]: ...
+
+class SupportsGetItemViewable(Protocol[_KT, _VT_co]):
+    def __len__(self) -> int: ...
+    def __iter__(self) -> Iterator[_KT]: ...
+    def __getitem__(self, key: _KT, /) -> _VT_co: ...
+
 # Unfortunately PEP 688 does not allow us to distinguish read-only
 # from writable buffers. We use these aliases for readability for now.
 # Perhaps a future extension of the buffer protocol will allow us to