Add support for complex address strings in back-compatibility mode

Yes you are right. It is a known and documented restriction on MailerHelperInterface::parseAddress(), so I would prefer to call it a feature request😃.

Since #3254085: Sending mails to multiple email addresses does not work via BC → , nearly a year ago, I've changed my views - back-compatibility mode is likely to stay around for many years, even "forever". So yes I am happy to fix this. We should use library code rather than re-inventing. I wonder about Mail_RFC822 in package pear/mail, see docs.

Thanks very much for the test. Setting to "Needs Review" so we can see that it fails😃.

In the meantime this patch solves the issue.

Also see swiftmailer_parse_mailboxes(), which is even more complex and yet still probably not fully correct or complete with the evolving standards.

Thanks the patch is useful for anyone who wants a solution in the meantime. I don't feel it's right to commit it, as it seems better to use library code.

See also core fix in 🐛 Uncaught RfcComplianceException when email From name contains a comma Fixed .

In my testing of splitting addresses, str_getcsv() is an improvement on explode() however it's not 100%:
- it works if the display name contains a comma
- if fails if the display name contains a less-than (because it removes the quotes within each address)