Fixes #2083 - Expose options for overriding the system appearance in the advanced settings menu

ElementX/Sources/Application/AppCoordinator.swift

@@ -167,6 +167,14 @@ class AppCoordinator: AppCoordinatorProtocol, AuthenticationCoordinatorDelegate,
         AnyView(
             navigationRootCoordinator.toPresentable()
                 .environment(\.analyticsService, ServiceLocator.shared.analytics)
+                .onReceive(appSettings.$appAppearance) { [weak self] appAppearance in
+                    guard let self else { return }
+                    
+                    windowManager.windows.forEach { window in
+                        // Unfortunately .preferredColorScheme doesn't propagate properly throughout the app when changed
+                        window.overrideUserInterfaceStyle = appAppearance.interfaceStyle
+                    }
+                }
         )
     }
     

ElementX/Sources/Application/AppSettings.swift

@@ -36,6 +36,7 @@ final class AppSettings {
         case otlpTracingEnabled
         case viewSourceEnabled
         case richTextEditorEnabled
+        case appAppearance
         
         case elementCallBaseURL
         case elementCallEncryptionEnabled
@@ -123,6 +124,9 @@ final class AppSettings {
     // A URL where users can go read more about the chat backup.
     let chatBackupDetailsURL: URL = "https://element.io/help#encryption5"
     
+    @UserPreference(key: UserDefaultsKeys.appAppearance, defaultValue: .system, storageType: .userDefaults(store))
+    var appAppearance: AppAppearance
+    
     // MARK: - Security
     
     /// The app must be locked with a PIN code as part of the authentication flow.

ElementX/Sources/Application/Windowing/WindowManager.swift

@@ -36,6 +36,10 @@ class WindowManager {
     /// A secondary window that can be presented instead of the main/overlay window combo.
     private(set) var alternateWindow: UIWindow!
     
+    var windows: [UIWindow] {
+        [mainWindow, overlayWindow, alternateWindow]
+    }
+    
     /// Configures the window manager to operate on the supplied scene.
     func configure(with windowScene: UIWindowScene) {
         mainWindow = windowScene.keyWindow