Refactor project structure and enhance functionality

Changed the project namespace from `Ghost.Editor` to `Ghost.App` across multiple files.
Changed the `InternalsVisibleTo` attribute in `AssemblyInfo.cs` to include `Ghost.App`.
Changed the `ProjectRepository` class to add new asynchronous methods for retrieving projects by ID, name, and metadata path.
Changed the `ProjectService` class to utilize the new asynchronous project loading methods.
Changed the `SceneGraph` classes to improve node management and serialization.
Changed the `EntityManager` class to enhance entity management with new component handling methods.
Added new test classes, `EntityTest` and `SerializationTest`, to ensure reliability in entity and serialization systems.
Added the `Ghost.App` project file to establish a modular project structure.
Added the `Ghost.Generator` project for automated component serialization code generation.
Updated UI components to reflect the new namespace for proper functionality.

Ghost.Editor/App.xaml.cs

@@ -1,102 +0,0 @@
-using Ghost.Editor.Helpers;
-using Ghost.Editor.Infrastructures.AppState;
-using Ghost.Editor.Services;
-using Microsoft.Extensions.DependencyInjection;
-using Microsoft.Extensions.Hosting;
-using Microsoft.UI.Xaml;
-using System;
-
-// To learn more about WinUI, the WinUI project structure,
-// and more about our project templates, see: http://aka.ms/winui-project-info.
-
-namespace Ghost.Editor
-{
-    /// <summary>
-    /// Provides application-specific behavior to supplement the default Application class.
-    /// </summary>
-    public partial class App : Application
-    {
-        private Window? _window;
-
-        internal static Window? Window
-        {
-            get => (Current as App)!._window;
-            set
-            {
-                if (Current is App app)
-                {
-                    app._window = value;
-                }
-            }
-        }
-
-        internal IHost Host
-        {
-            get;
-        }
-
-        /// <summary>
-        /// Initializes the singleton application object.  This is the first line of authored code
-        /// executed, and as such is the logical equivalent of main() or WinMain().
-        /// </summary>
-        internal App()
-        {
-            InitializeComponent();
-
-            Host = Microsoft.Extensions.Hosting.Host.
-                CreateDefaultBuilder().
-                UseContentRoot(AppContext.BaseDirectory).
-                ConfigureServices((context, services) =>
-                {
-                    HostHelper.AddLandingScope(context, services);
-                    HostHelper.AddEngineScope(context, services);
-
-                    services.AddSingleton<AppStateMachine>();
-                    services.AddSingleton<StackedNotificationService>();
-                })
-                .Build();
-
-            UnhandledException += App_UnhandledException;
-        }
-
-        internal static IServiceScope CreateScope()
-        {
-            return (Current as App)!.Host.Services.CreateScope();
-        }
-
-        public static T GetService<T>() where T : class
-        {
-            if ((Current as App)!.Host.Services.GetService(typeof(T)) is not T service)
-            {
-                throw new ArgumentException($"{typeof(T)} needs to be registered in ConfigureServices within App.xaml.cs.");
-            }
-
-            return service;
-        }
-
-        /// <summary>
-        /// Invoked when the application is launched.
-        /// </summary>
-        /// <param name="args">Details about the launch request and process.</param>
-        protected override async void OnLaunched(LaunchActivatedEventArgs args)
-        {
-            base.OnLaunched(args);
-
-            ActivationHandler.Handle(args);
-
-            Host.Start();
-
-            var stateMachine = GetService<AppStateMachine>();
-            stateMachine.RegisterState(StateKey.Landing, () => new LandingState());
-            stateMachine.RegisterState(StateKey.EngineEditor, () => new EditorState());
-
-            await stateMachine.TransitionToAsync(StateKey.Landing);
-        }
-
-        private void App_UnhandledException(object sender, Microsoft.UI.Xaml.UnhandledExceptionEventArgs e)
-        {
-            // TODO: Log and handle exceptions as appropriate.
-            // https://docs.microsoft.com/windows/windows-app-sdk/api/winrt/microsoft.ui.xaml.application.unhandledexception.
-        }
-    }
-}