net/mail: treat comment in address as display name
I verified this change on a corpus of > 200 GB of emails since the mid-90s. With
this change, more addresses parse than before, and anything which parsed before
still parses.
In said corpus, I came across the edge case of comments preceding an
addr-spec (with angle brackets!), e.g. “(John Doe) <john@example.com>”, which
does not satisfy the conditions to be treated as a fallback, as per my reading
of RFC2822.
This change does not parse quoted-strings within comments (a corresponding TODO
is in the code), but I have not seen that in the wild.