[3.13] gh-130631: Make join_header_words() more similar to the original Perl version (GH-130632) (GH-132303)

* Always quote strings with non-ASCII characters.
* Allow some non-separator and non-control characters (like "." or "-")
  be unquoted.
* Always quote strings that end with "\n".
* Use the fullmatch() method for clarity and optimization.
(cherry picked from commit 7ebbd271444d89218870169624921b795a717470)