What are the default special folder names for IMAP accounts in Mail.app (like Drafts, Junk, Sent)?
The Internet Engineering Task Force (IETF) defines that in a proper RFC, the RFC 6154. There you will find a list of special use mailbox denominations:

   \All
      This mailbox presents all messages in the user's message store.
      Implementations MAY omit some messages, such as, perhaps, those
      in \Trash and \Junk.  When this special use is supported, it is
      almost certain to represent a virtual mailbox.

   \Archive
        This mailbox is used to archive messages.  The meaning of an
        "archival" mailbox is server-dependent; typically, it will be
        used to get messages out of the inbox, or otherwise keep them
        out of the user's way, while still making them accessible.

   \Drafts
        This mailbox is used to hold draft messages -- typically,
        messages that are being composed but have not yet been sent.  In
        some server implementations, this might be a virtual mailbox,
        containing messages from other mailboxes that are marked with
        the "\Draft" message flag.  Alternatively, this might just be
        advice that a client put drafts here.

   \Flagged
        This mailbox presents all messages marked in some way as
        "important".  When this special use is supported, it is likely
        to represent a virtual mailbox collecting messages (from other
        mailboxes) that are marked with the "\Flagged" message flag.

   \Junk
        This mailbox is where messages deemed to be junk mail are held.
        Some server implementations might put messages here
        automatically.  Alternatively, this might just be advice to a
        client-side spam filter.

   \Sent
        This mailbox is used to hold copies of messages that have been
        sent.  Some server implementations might put messages here
        automatically.  Alternatively, this might just be advice that a
        client save sent messages here.

   \Trash
        This mailbox is used to hold messages that have been deleted or
        marked for deletion.  In some server implementations, this might
        be a virtual mailbox, containing messages from other mailboxes
        that are marked with the "\Deleted" message flag.
        Alternatively, this might just be advice that a client that
        chooses not to use the IMAP "\Deleted" model should use this as
        its trash location.  In server implementations that strictly
        expect the IMAP "\Deleted" model, this special use is likely not
        to be supported.