Reply rendering (#861)

* Cleanup how we use message timeline items in preparation for rich reply rendering

* Expose reply details up to the UI level

* Render replies in the timeline (textual for now). Remove now unused AttributedStringBuilderComponent isReply flag.

* Move reply detail loading to when the item appears instead of when it's created.

* Fix unit tests

* Fetch event details also when the reply details are in the error state

* Tweaks following code review

* Localise emote bodies

* Fix replies not loading sometimes, use the current event identifier instead of the one being replied to

ElementX/Sources/Services/Timeline/TimelineItemProxy.swift

@@ -65,15 +65,7 @@ struct EventTimelineItemProxy {
             return .sent(elapsedTime: Date().timeIntervalSince1970 - timestamp.timeIntervalSince1970)
         }
     }
-    
-    var body: String? {
-        content.asMessage()?.body()
-    }
-    
-    var isMessage: Bool {
-        content.asMessage() != nil
-    }
-    
+        
     var isRoomState: Bool {
         content.kind().isRoomState
     }