bpo-41818: Add termios.tcgetwinsize(), termios.tcsetwinsize(). Update docs.

[8vasu]

This follows #23536. Also, see #23546, #23740.

tcgetwinsize() and tcsetwinsize() are expected to appear in IEEE Std 1003.1 ("POSIX.1") issue 8 [ the upcoming version of POSIX ] as declarations in <termios.h>; see https://www.austingroupbugs.net/view.php?id=1151#c3856.

NetBSD already has them (thanks to user "kre"):

1. http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/termios/tcgetwinsize.c?only_with_tag=MAIN
2. http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/termios/tcsetwinsize.c?only_with_tag=MAIN

Update: musl libc also has these functions.
Update2: The patches that I had submitted to add tcgetwinsize() and tcsetwinsize() to the FreeBSD libc have been merged. I am still working on getting them included in glibc.

When POSIX.1 issue 8 is released, termios.tcgetwinsize(), termios.tcsetwinsize() can be updated to utilize the native versions.

Post #23686, #23546, #23740 goals:

1. add test_winsize() to "Lib/test/test_pty.py";
2. major revision of "Lib/pty.py", which has not happened since the beginning of the millennium.

Signed-off-by: Soumendra Ganguly soumendraganguly@gmail.com

https://bugs.python.org/issue41818