Introduce view model for thread title view

Riot/Modules/Room/Views/Title/Thread/ThreadRoomTitleViewModel.swift

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+// 
+// Copyright 2021 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import Foundation
+
+struct ThreadRoomTitleViewModel {
+    var roomAvatar: AvatarViewDataProtocol?
+    var roomEncryptionBadge: UIImage?
+    var roomDisplayName: String?
+    
+    static let empty = ThreadRoomTitleViewModel(roomAvatar: nil,
+                                                roomEncryptionBadge: nil,
+                                                roomDisplayName: nil)
+}