bpo-28556: Various updates to typing (#28) (#77)

various updates from upstream python/typing repo:

- Added typing.Counter and typing.ChainMap generics
- More flexible typing.NamedTuple
- Improved generic ABC caching
- More tests
- Bugfixes
- Other updates
* Add Misc/NEWS entry


(cherry picked from commit b692dc8475a032740576129d0990ddc3edccab2b)
4 files changed