RFC: https://wiki.php.net/rfc/enumerations

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

Closes GH-6489.

* PHP-8.0:
  Fix #80751: Comma in recipient name breaks email delivery

* PHP-7.4:
  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.

* PHP-8.0:
  Avoid C4090 level 1 warning

* PHP-7.4:
  Avoid C4090 level 1 warning

This breaks the build for PHP 8 by default.

* PHP-8.0:
  Fix #80706: mail(): Headers after Bcc headers may be ignored

* PHP-7.4:
  Fix #80706: mail(): Headers after Bcc headers may be ignored

We need to handle the case where a CRLF after a Bcc header is not the
beginning of a folding marker, because in that case the Bcc header was
not the last "thing".

Closes GH-6666.