Add Authentication Flow WIP.

- Add Registration Screen.
- Add Server Selection Screen.
- Rename AuthenticationCoordinator to LegacyAuthenticationCoordinator.
- Add AuthenticationService and RegistrationWizard.
- Async extensions.
- Add global white and EMS colors to the themes.
- Add tests for server selection and registration screens.
- Accessibility and iPad layout tweaks.
- Remove MainActor from Auth Coordinators/VMs/Views.
(It broke the protocol conformances so now the methods and properties are marked individually.)

RiotSwiftUI/Modules/Authentication/ServerSelection/AuthenticationServerSelectionModels.swift

@@ -0,0 +1,77 @@
+// 
+// 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
+
+// MARK: View model
+
+enum AuthenticationServerSelectionViewModelResult {
+    /// The user would like to use the homeserver at the given address.
+    case next(homeserverAddress: String)
+    /// Dismiss the view without using the entered address.
+    case dismiss
+}
+
+// MARK: View
+
+struct AuthenticationServerSelectionViewState: BindableState {
+    /// View state that can be bound to from SwiftUI.
+    var bindings: AuthenticationServerSelectionBindings
+    /// An error message to be shown in the text field footer.
+    var footerErrorMessage: String?
+    /// Whether the screen is presented modally or within a navigation stack.
+    var hasModalPresentation: Bool
+    
+    /// The message to show in the text field footer.
+    var footerMessage: String {
+        footerErrorMessage ?? VectorL10n.authenticationServerSelectionServerFooter
+    }
+    
+    /// The text field is showing an error.
+    var isShowingFooterError: Bool {
+        footerErrorMessage != nil
+    }
+    
+    /// Whether it is possible to continue by tapping the Next button.
+    var hasValidationError: Bool {
+        bindings.homeserverAddress.isEmpty || isShowingFooterError
+    }
+}
+
+struct AuthenticationServerSelectionBindings: BindableState {
+    /// The homeserver address input by the user.
+    var homeserverAddress: String
+    /// Information describing the currently displayed alert.
+    var alertInfo: AlertInfo<AuthenticationServerSelectionErrorType>?
+}
+
+enum AuthenticationServerSelectionViewAction {
+    /// The user would like to use the homeserver at the input address.
+    case next
+    /// Dismiss the view without using the entered address.
+    case dismiss
+    /// Open the EMS link.
+    case getInTouch
+    /// Clear any errors shown in the text field footer.
+    case clearFooterError
+}
+
+enum AuthenticationServerSelectionErrorType: Hashable {
+    /// An error message to be shown in the text field footer.
+    case footerMessage(String)
+    /// An error occurred when trying to open the EMS link
+    case openURLAlert
+}