Add onboarding avatar screen.

Includes a PhotoPickerPresenter to pick photos without requesting permissions.

RiotSwiftUI/Modules/Onboarding/Avatar/OnboardingAvatarModels.swift

@@ -0,0 +1,51 @@
+// 
+// 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 UIKit
+
+// MARK: View model
+
+enum OnboardingAvatarViewModelResult {
+    case pickImage
+    case takePhoto
+    case save(UIImage?)
+    case skip
+}
+
+// MARK: View
+
+struct OnboardingAvatarViewState: BindableState {
+    let placeholderAvatarLetter: String
+    let placeholderAvatarColorIndex: Int
+    var avatar: UIImage?
+    var isWaiting = false
+    var bindings: OnboardingAvatarBindings
+    
+    var buttonImage: ImageAsset {
+        avatar == nil ? Asset.Images.onboardingAvatarCamera : Asset.Images.onboardingAvatarEdit
+    }
+}
+
+struct OnboardingAvatarBindings {
+    var alertInfo: AlertInfo<Int>?
+}
+
+enum OnboardingAvatarViewAction {
+    case pickImage
+    case takePhoto
+    case save
+    case skip
+}