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/Room/RoomSummary/RoomEventStringBuilder.swift

@@ -45,7 +45,7 @@ struct RoomEventStringBuilder {
             // Message types that don't need a prefix.
             case .emote(content: let content):
                 let senderDisplayName = sender.displayName ?? sender.id
-                return AttributedString("* \(senderDisplayName) \(content.body)")
+                return AttributedString(L10n.commonEmote(senderDisplayName, content.body))
             // Message types that should be prefixed with the sender's name.
             case .image:
                 message = L10n.commonImage