Support IMAP4 Rev 2

Support IMAP 4 Rev 2 (RFC-9051).

A compatibility notice is available here: https://datatracker.ietf.org/doc/html/rfc9051#appendix-E

Here is a list of actions needed:

• Advertise IMAP4Rev2 capability and support enabling it.
• LIST-EXTENDED [RFC5258]
• LIST-STATUS [RFC5819]
• Response codes [RFC5530]
• FETCH side of the BINARY extension [RFC3516]
• List of new mailbox attributes from SPECIAL-USE [RFC6154]
• STATUS SIZE [RFC8438]
• STATUS DELETED cf https://datatracker.ietf.org/doc/html/rfc9051#section-6.3.11
• SELECT/EXAMINE are now required to return an untagged LIST response.
• Clarified that the server doesn't need to send a new PERMANENTFLAGS response code when a new keyword was successfully added and the server advertised * earlier for the same mailbox.
• Mailbox names and message headers now allow for UTF-8.
• All unsolicited FETCH updates are required to include UID.
• Required COPY/MOVE to return the TRYCREATE response code, if the target mailbox doesn't exist and can be created.

Open question: how to test inter operability / conformity?

• Use clients that are IMAP4Rev2 compliant?
• Find some IMAP4Rev2 test suite in the wild?