Fix #80751: Comma in recipient name breaks email delivery

Fix #80751: Comma in recipient name breaks email delivery

So far, `SendText()` simply separates potential email address lists at
any comma, disregarding that commas inside a quoted-string do not
delimit addresses.  We fix that by introducing an own variant of
`strtok_r()` which caters to quoted-strings.

We also make `FormatEmailAddress()` aware of quoted strings.

We do not cater to email address comments, and potentially other quirks
of RFC 5322 email addresses, but catering to quoted-strings is supposed
to solve almost all practical use cases.

Co-authored-by: Nikita Popov <nikita.ppv@gmail.com>
Closes GH-6735.