macro Py_SETREF.

Patch includes contributions by Isobel Hooper, incorporating suggestions from
Paul Winkler.  Reviewed by Martin Panter.

In addition to accepting the corrections for the RFC compliance wording, I
went through and corrected all the argument and return types, and made the
pattern of how the arguments and return types are documented consistent.
So, this patch also addresses #20782, though I had forgotten about that issue
and its patch.

os.fwalk() parameter names.

Original patch by Samson Lee.

Added tests for dict views iterators.

This allows sys.getsize() to work correctly with their subclasses with
__slots__ defined.

to ASCII replacements.  Original patch by Chris Angelico.

Added test for return code for the last RegQueryValueExW.

Initial patch by SilentGhost