feat: add ability to change app icon

Add ability to change application icon to any image file inside the src\Ryujinx\Assets\Icons\AppIcons directory. The app should automatically load any resource in that folder as a selectable icon.

src/Ryujinx/Systems/Configuration/ConfigurationState.Model.cs

@@ -150,6 +150,11 @@ namespace Ryujinx.Ava.Systems.Configuration
             /// </summary>
             public ReactiveObject<string> BaseStyle { get; private set; }
 
+            /// <summary>
+            /// The currently selected window icon.
+            /// </summary>
+            public ReactiveObject<string> SelectedWindowIcon { get; private set; }
+
             /// <summary>
             /// Start games in fullscreen mode
             /// </summary>
@@ -199,6 +204,7 @@ namespace Ryujinx.Ava.Systems.Configuration
                 ShownFileTypes = new ShownFileTypeSettings();
                 WindowStartup = new WindowStartupSettings();
                 BaseStyle = new ReactiveObject<string>();
+                SelectedWindowIcon = new ReactiveObject<string>();
                 StartFullscreen = new ReactiveObject<bool>();
                 StartNoUI = new ReactiveObject<bool>();
                 GameListViewMode = new ReactiveObject<int>();