Offer {Resource,Node,Domain}Ref on Jid API

This provides a non-copying API, which is generally favourable. The
other accessors were removed, because the intent was to provide this
"most sensible" API via the "default" (i.e. shortest, most concisely
named) functions.

xmpp/src/message/receive/chat.rs

@@ -39,7 +39,7 @@ pub async fn handle_message_chat<C: ServerConnector>(
                     Jid::Full(full) => Event::RoomPrivateMessage(
                         message.id.clone(),
                         full.to_bare(),
-                        full.resource_str().to_owned(),
+                        full.resource().to_string(),
                         body.clone(),
                         time_info.clone(),
                     ),

xmpp/src/message/receive/group_chat.rs

@@ -21,7 +21,7 @@ pub async fn handle_message_group_chat<C: ServerConnector>(
     if let Some((_lang, subject)) = message.get_best_subject(langs.clone()) {
         events.push(Event::RoomSubject(
             from.to_bare(),
-            from.resource_str().map(String::from),
+            from.resource().map(|x| x.to_string()),
             subject.0.clone(),
             time_info.clone(),
         ));
@@ -32,7 +32,7 @@ pub async fn handle_message_group_chat<C: ServerConnector>(
             Jid::Full(full) => Event::RoomMessage(
                 message.id.clone(),
                 from.to_bare(),
-                full.resource_str().to_owned(),
+                full.resource().to_string(),
                 body.clone(),
                 time_info,
             ),