[1.7.x] Fixed #23639 -- Fixed doc error in RegexValidator.regex

Thanks to @claudep for the report and the original patch.

Backport of c48a29a02a457cfdb1cff11009401459ba24e870 from master.
[1.7.x] Fixed #23063 -- Convert \n and \r to \r\n when using the SMTP backend as per RFC.

Backport of 8d789449c7861b8cf8b10d244f26d9d354989aaf from master.