Refactor project from Ghost.App to Ghost.Editor

Changed the project structure to reflect a shift from `Ghost.App` to `Ghost.Editor`, updating namespaces and class names throughout.

Changed the application class in `App.xaml` and `App.xaml.cs` from `GhostApplication` to `EditorApplication`.

Changed several service interfaces to reside under `Ghost.Editor.Services.Contracts`, including `IInspectorService`, `INotificationService`, and `IProgressService`.

Added `InspectorView` and `InspectorViewModel` classes to manage inspector functionality.

Added `NavigationTabView` and `NavigationTabPage` classes to facilitate navigation within the editor.

Enhanced `WorldNode` and `EntityNode` classes to support scene graph functionality, including serialization and entity management.

Updated the project file `Ghost.Editor.csproj` to reflect the new structure and removed old references.

Modified the solution file `GhostEngine.sln` to remove references to `Ghost.App` and include `Ghost.Editor`.

Updated unit tests to align with the new namespaces and project structure.

Ghost.App/Core/AppState/LandingState.cs

@@ -0,0 +1,45 @@
+using Ghost.Editor;
+using Ghost.Editor.View.Windows;
+using System.Threading.Tasks;
+
+namespace Ghost.Editor.Core.AppState;
+
+internal class LandingState : IAppState
+{
+    private LandingWindow? _window;
+
+    public Task OnExitingAsync()
+    {
+        if (EditorApplication.Window == _window)
+        {
+            EditorApplication.Window = null;
+        }
+        return Task.CompletedTask;
+    }
+
+    public Task OnEnteringAsync(object? parameter)
+    {
+        _window = EditorApplication.GetService<LandingWindow>();
+        EditorApplication.Window = _window;
+
+        _window.Activate();
+        return Task.CompletedTask;
+    }
+
+    public Task OnExitedAsync()
+    {
+        if (EditorApplication.Window == _window)
+        {
+            EditorApplication.Window = null;
+        }
+
+        _window?.Close();
+        _window = null;
+        return Task.CompletedTask;
+    }
+
+    public Task OnEnteredAsync(object? parameter)
+    {
+        return Task.CompletedTask;
+    }
+}