Start to port main gut of the foundation

Toolkit.Foundation/Lifecycles/AppService.cs

@@ -0,0 +1,29 @@
+using CommunityToolkit.Mvvm.Messaging;
+using Microsoft.Extensions.Hosting;
+
+namespace Toolkit.Foundation
+{
+    public class AppService : IHostedService
+    {
+        private readonly IMessenger messenger;
+        private readonly IInitialization initialization;
+
+        public AppService(IMessenger messenger,
+            IInitialization initialization)
+        {
+            this.messenger = messenger;
+            this.initialization = initialization;
+        }
+
+        public async Task StartAsync(CancellationToken cancellationToken)
+        {
+            messenger.Send(new Initialize());
+            await initialization.InitializeAsync();
+        }
+
+        public Task StopAsync(CancellationToken cancellationToken)
+        {
+            return Task.CompletedTask;
+        }
+    }
+}