RFC5258 (2008): `LIST-EXTENDED` (mostly included in `IMAP4rev2`)

[nevans]

RFC5258 also established an IANA registy.

• [ ] Add select options to #list, using RFC4466 tagged-ext syntax
• [ ] Add return options to #list, using RDC4466 tagged-ext syntax
• [ ] Parse all RFC9051 mbox-list-extended-item directly
  • TODO: add appropriate tickets here...
• [ ] Parse all other mbox-list-extended-item extensions directly
  • TODO: add appropriate tickets here...
• [ ] Parse unknown mbox-list-extended into TaggedExtensionData