Add onboarding avatar screen.

Includes a PhotoPickerPresenter to pick photos without requesting permissions.

RiotSwiftUI/Modules/Onboarding/Avatar/OnboardingAvatarViewModelProtocol.swift

@@ -0,0 +1,29 @@
+// 
+// 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 SwiftUI
+
+protocol OnboardingAvatarViewModelProtocol {
+    
+    var completion: ((OnboardingAvatarViewModelResult) -> Void)? { get set }
+    @available(iOS 14, *)
+    var context: OnboardingAvatarViewModelType.Context { get }
+    
+    func updateAvatarImage(with image: UIImage?)
+    
+    func startLoading()
+    func stopLoading(error: Error?)
+}