Major Description
The goal is to convert the ACL list into mailbox list.
We need to add a Mailbox feature ACLMailboxSearch. When the feature is supported, MailboxManager::search will also return mailboxes I have the delegated rights on.
Beware: the MailboxSearchQuery does not express this kind of search yet (A mailbox path like"":"":"" seems to have the wanted behaviour)
We need to store "per user delegated mailboxes" and inject them as part of the MailboxMapper::findMailboxWithPathLike seems the right place to handle this. (We then need to handle special case empty namespace and empty username as per today code organisation).