feat: Move all encrypted messages to mvbox if MvboxMove is on

Before, only replies to chat messages were moved to the mvbox because we're removing Chat-Version
from outer headers, but there's no much sense in moving only replies and not moving original
messages and MDNs. Instead, move all encrypted messages. Users should be informed about this in UIs,
so if a user has another PGP-capable MUA, probably they should disable MvboxMove. Moreover, untying
this logic from References and In-Reply-To allows to remove them from outer headers too, the "Header
Protection for Cryptographically Protected Email" RFC even suggests such a behavior:
https://datatracker.ietf.org/doc/html/rfc9788#name-offering-more-ambitious-hea.

src/imap.rs

@@ -2106,17 +2106,7 @@ async fn needs_move_to_mvbox(
         // there may be a non-delta device that wants to handle it
         return Ok(false);
     }
-
-    if headers.get_header_value(HeaderDef::SecureJoin).is_some() {
-        Ok(true)
-    } else if let Some(parent) = get_prefetch_parent_message(context, headers).await? {
-        match parent.is_dc_message {
-            MessengerMessage::No => Ok(false),
-            MessengerMessage::Yes | MessengerMessage::Reply => Ok(true),
-        }
-    } else {
-        Ok(false)
-    }
+    Ok(headers.get_header_value(HeaderDef::SecureJoin).is_some() || is_encrypted(headers))
 }
 
 /// Try to get the folder meaning by the name of the folder only used if the server does not support XLIST.

src/imap/imap_tests.rs

@@ -171,7 +171,7 @@ const COMBINATIONS_ACCEPTED_CHAT: &[(&str, bool, bool, &str)] = &[
     ("INBOX", false, false, "INBOX"),
     ("INBOX", false, true, "INBOX"),
     ("INBOX", true, false, "INBOX"),
-    ("INBOX", true, true, "INBOX"),
+    ("INBOX", true, true, "DeltaChat"),
     ("Spam", false, false, "INBOX"),
     ("Spam", false, true, "INBOX"),
     // Move unencrypted emails in accepted chats from Spam to INBOX, not 100% sure on this, we could
@@ -185,7 +185,7 @@ const COMBINATIONS_REQUEST: &[(&str, bool, bool, &str)] = &[
     ("INBOX", false, false, "INBOX"),
     ("INBOX", false, true, "INBOX"),
     ("INBOX", true, false, "INBOX"),
-    ("INBOX", true, true, "INBOX"),
+    ("INBOX", true, true, "DeltaChat"),
     ("Spam", false, false, "Spam"),
     ("Spam", false, true, "INBOX"),
     ("Spam", true, false, "Spam"),