infra: Make Avalonia the default UI (#6375)

* misc: Move Ryujinx project to Ryujinx.Gtk3

This breaks release CI for now but that's fine.

Signed-off-by: Mary Guillemard <mary@mary.zone>

* misc: Move Ryujinx.Ava project to Ryujinx

This breaks CI for now, but it's fine.

Signed-off-by: Mary Guillemard <mary@mary.zone>

* infra: Make Avalonia the default UI

Should fix CI after the previous changes.

GTK3 isn't build by the release job anymore, only by PR CI.

This also ensure that the test-ava update package is still generated to
allow update from the old testing channel.

Signed-off-by: Mary Guillemard <mary@mary.zone>

* Fix missing copy in create_app_bundle.sh

Signed-off-by: Mary Guillemard <mary@mary.zone>

* Fix syntax error

Signed-off-by: Mary Guillemard <mary@mary.zone>

---------

Signed-off-by: Mary Guillemard <mary@mary.zone>

src/Ryujinx/UI/Applet/ErrorAppletWindow.axaml.cs

@@ -0,0 +1,74 @@
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Threading;
+using Ryujinx.Ava.Common.Locale;
+using Ryujinx.Ava.UI.Windows;
+using System.Threading.Tasks;
+
+namespace Ryujinx.Ava.UI.Applet
+{
+    internal partial class ErrorAppletWindow : StyleableWindow
+    {
+        private readonly Window _owner;
+        private object _buttonResponse;
+
+        public ErrorAppletWindow(Window owner, string[] buttons, string message)
+        {
+            _owner = owner;
+            Message = message;
+            DataContext = this;
+            InitializeComponent();
+
+            int responseId = 0;
+
+            if (buttons != null)
+            {
+                foreach (string buttonText in buttons)
+                {
+                    AddButton(buttonText, responseId);
+                    responseId++;
+                }
+            }
+            else
+            {
+                AddButton(LocaleManager.Instance[LocaleKeys.InputDialogOk], 0);
+            }
+        }
+
+        public ErrorAppletWindow()
+        {
+            DataContext = this;
+            InitializeComponent();
+        }
+
+        public string Message { get; set; }
+
+        private void AddButton(string label, object tag)
+        {
+            Dispatcher.UIThread.InvokeAsync(() =>
+            {
+                Button button = new() { Content = label, Tag = tag };
+
+                button.Click += Button_Click;
+                ButtonStack.Children.Add(button);
+            });
+        }
+
+        private void Button_Click(object sender, RoutedEventArgs e)
+        {
+            if (sender is Button button)
+            {
+                _buttonResponse = button.Tag;
+            }
+
+            Close();
+        }
+
+        public async Task<object> Run()
+        {
+            await ShowDialog(_owner);
+
+            return _buttonResponse;
+        }
+    }
+}