Wait for the session restore in background app refresh

When iOS relaunches a terminated app for the task, the session is still
being restored asynchronously when the refresh starts. Wait up to 5
seconds for the restore to finish, bailing out early if the app isn't
restoring a session (e.g. signed out or the restore failed).

# Conflicts:
#	ElementX/Sources/Application/AppCoordinator.swift

ElementX/Sources/Application/AppCoordinator.swift

@@ -1302,7 +1302,11 @@ private extension AppCoordinator {
             }
         }
         
+        await waitForSessionRestore()
+        
         guard let userSession else {
+            MXLog.info("Background app refresh: no user session, giving up.")
+            task.setTaskCompleted(success: false)
             return
         }
         
@@ -1393,3 +1397,15 @@ private extension AppCoordinator {
         task.setTaskCompleted(success: true)
     }
 }
+
+private extension AppCoordinator {
+    /// When iOS relaunches a terminated app for a background task, the session is still being restored asynchronously.
+    func waitForSessionRestore() async {
+        let deadline = ContinuousClock.now + .seconds(5)
+        while userSession == nil,
+              stateMachine.state == .initial || stateMachine.state == .restoringSession,
+              ContinuousClock.now < deadline {
+            try? await Task.sleep(for: .milliseconds(100))
+        }
+    }
+}