Refactor application structure and add unit tests

Added:
- New `ProgressService` class for managing progress indicators.
- New `AssetDatabase`, `AssetOpenHandlerAttribute`, and `AsyncAssetOpenHandlerAttribute` classes for asset handling.
- `Ghost.UnitTest` project for unit testing with associated files and configurations.

Changed:
- `ActivationHandler` class to ensure correct handling of `LaunchActivatedEventArgs`.
- `App.xaml.cs` to register `INotificationService` and `IProgressService`, replacing `StackedNotificationService`.
- `OnLaunched` method in `App.xaml.cs` to correctly call `ActivationHandler.Handle(args)` and start the host.
- `INavigationAware` interface from internal to public for broader access.
- `EditorState.cs` to activate `EditorApplication` with the current service provider.
- Property names in `AssetItem` and `ExplorerItem` structs to `Name` and `FullName`.
- `NotificationService` class to implement `INotificationService` and refactor notification handling.
- `AssetPathToGlyphConverter` to handle file extensions consistently.
- Bindings in `ProjectPage.xaml` and `ProjectPage.xaml.cs` to use `FullName` instead of `Path`.
- `EngineEditorWindow` and `LandingWindow` classes to utilize new notification and progress services.
- `Logger` class to include a new method for logging errors with exceptions.

Updated:
- Manifest files and project files to reflect new structure and dependencies.
- Solution file `GhostEngine.sln` to include the new unit test project.
- Added several new test classes and methods in `UnitTests.cs`.

Ghost.App/View/Pages/EngineEditor/HierarchyPage.xaml.cs

@@ -0,0 +1,57 @@
+using Ghost.Editor.SceneGraph;
+using Ghost.Editor.ViewModels.Pages.EngineEditor;
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+
+// To learn more about WinUI, the WinUI project structure,
+// and more about our project templates, see: http://aka.ms/winui-project-info.
+
+namespace Ghost.App.View.Pages.EngineEditor;
+/// <summary>
+/// An empty page that can be used on its own or navigated to within a Frame.
+/// </summary>
+internal sealed partial class HierarchyPage : Page
+{
+    public HierarchyViewModel ViewModel
+    {
+        get;
+    }
+
+    public HierarchyPage()
+    {
+        ViewModel = GhostApplication.GetService<HierarchyViewModel>();
+
+        InitializeComponent();
+    }
+}
+
+internal partial class HierarchyTemplateSector : DataTemplateSelector
+{
+    public DataTemplate? WorldTemplate
+    {
+        get;
+        set;
+    }
+
+    public DataTemplate? EntityTemplate
+    {
+        get;
+        set;
+    }
+
+    protected override DataTemplate SelectTemplateCore(object item)
+    {
+        if (WorldTemplate == null || EntityTemplate == null)
+        {
+            return base.SelectTemplateCore(item);
+        }
+
+        var node = (SceneGraphNode)item;
+        return node.NodeType switch
+        {
+            SceneGraphNodeType.Scene => WorldTemplate,
+            SceneGraphNodeType.Entity => EntityTemplate,
+            _ => base.SelectTemplateCore(item)
+        };
+    }
+}