[3.9] gh-80222: Fix email address header folding with long quoted-string (GH-122753...

[3.9] gh-80222: Fix email address header folding with long quoted-string (GH-122753) (GH-129111) (GH-132371)

Email generators using email.policy.default could incorrectly omit the
quote ('"') characters from a quoted-string during header refolding,
leading to invalid address headers and enabling header spoofing. This
change restores the quote characters on a bare-quoted-string as the
header is refolded, and escapes backslash and quote chars in the string.

(cherry picked from commit 5aaf4168583)
(cherry picked from commit a4ef689ce670684ec132204b1cd03720c8e0a03d)

Co-authored-by: R. David Murray <rdmurray@bitdance.com>
Co-authored-by: Mike Edmunds <medmunds@gmail.com>
Co-authored-by: Łukasz Langa <lukasz@langa.pl>