bpo-42163, bpo-42189, bpo-42659: Support uname_tuple._replace (for all but processor...

bpo-42163, bpo-42189, bpo-42659: Support uname_tuple._replace (for all but processor) (#23010)

* Add test capturing missed expectation with uname_result._replace.

* bpo-42163: Override uname_result._make to allow uname_result._replace to work (for everything but 'processor'.

* Replace hard-coded length with one derived from the definition.

* Add test capturing missed expectation with copy/deepcopy on namedtuple (bpo-42189).

* bpo-42189: Exclude processor parameter when constructing uname_result.

* In _make, rely on __new__ to strip processor.

* Add blurb.

* iter is not necessary here.

* Rely on num_fields in __new__

* Add test for slices on uname

* Add test for copy and pickle.

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
* import pickle

* Fix equality test after pickling.

* Simply rely on __reduce__ for pickling.

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>