gh-59705: Add _thread.set_name() function (#127338)

On Linux, threading.Thread now sets the thread name to the operating
system.

* configure now checks if pthread_getname_np()
  and pthread_setname_np() functions are available.
* Add PYTHREAD_NAME_MAXLEN macro.
* Add _thread._NAME_MAXLEN constant for test_threading.

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