Add the inviter to JoinRoomScreen when it's an invite. (#3093)

* Add inviter property to RoomProxyProtocol.

* Extract the room cell inviter label into it's own view.

* Use the new RoomInviterLabel in the JoinRoomScreen.

* Fix bug with invite to a public room.

ElementX/Sources/Services/Room/RoomProxyProtocol.swift

@@ -40,6 +40,7 @@ protocol RoomProxyProtocol {
     var isFavourite: Bool { get async }
     var pinnedEventIDs: [String] { get async }
     var membership: Membership { get }
+    var inviter: RoomMemberProxyProtocol? { get async }
     var hasOngoingCall: Bool { get }
     var canonicalAlias: String? { get }
     var ownUserID: String { get }