Introduce an AppMediator which will:

- combine multiple services to handle app wide requests
- remove direct UIApplication access from everywhere
- fix #2703 by combining UIApplication.applicationState with the WindowManager's main window appearance
- leave the door open for more app control in the future (especiall for the mac)

ElementX/Sources/Application/AppMediatorProtocol.swift

@@ -0,0 +1,63 @@
+//
+// Copyright 2022 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
+import UIKit
+
+// sourcery: AutoMockable
+protocol AppMediatorProtocol {
+    func beginBackgroundTask(withName taskName: String?, expirationHandler handler: (() -> Void)?) -> UIBackgroundTaskIdentifier
+
+    func endBackgroundTask(_ identifier: UIBackgroundTaskIdentifier)
+    
+    func open(_ url: URL)
+    
+    func openAppSettings()
+
+    var backgroundTimeRemaining: TimeInterval { get }
+
+    var appState: UIApplication.State { get }
+}
+
+extension UIApplication.State: CustomStringConvertible {
+    public var description: String {
+        switch self {
+        case .active:
+            return "active"
+        case .inactive:
+            return "inactive"
+        case .background:
+            return "background"
+        @unknown default:
+            return "unknown"
+        }
+    }
+}
+
+extension UIUserInterfaceActiveAppearance: CustomStringConvertible {
+    public var description: String {
+        switch self {
+        case .active:
+            return "active"
+        case .inactive:
+            return "inactive"
+        case .unspecified:
+            return "unspecified"
+        @unknown default:
+            return "unknown"
+        }
+    }
+}