Setup Wizard restructuring

- Remove polymorphic base, this only existed because TKMM has a desktop/switch setup prodecure difference and has 2 implementations of the setup wizard. We only need one.
- Remove Systems/UI file split, they're all in Ryujinx.Ava.UI now
- made NotificationHelper instance-based to allow you to encapsulate notifications to a window that magically disappear when the window is closed, instead of switching to showing on the main window.

src/Ryujinx/UI/SetupWizard/Pages/Keys/SetupKeysPageContext.cs

@@ -0,0 +1,98 @@
+using Avalonia.Controls;
+using Avalonia.Platform.Storage;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using DynamicData;
+using Gommon;
+using Ryujinx.Ava.Common.Locale;
+using Ryujinx.Ava.Utilities;
+using Ryujinx.Common.Configuration;
+using Ryujinx.Common.Logging;
+using Ryujinx.HLE.Exceptions;
+using Ryujinx.HLE.FileSystem;
+using System;
+using System.IO;
+using System.Threading.Tasks;
+
+namespace Ryujinx.Ava.UI.SetupWizard.Pages
+{
+    public partial class SetupKeysPageContext : SetupWizardPageContext
+    {
+        public override Result CompleteStep() =>
+            !Directory.Exists(KeysFolderPath)
+                ? Result.Fail 
+                : InstallKeys(KeysFolderPath);
+
+        [ObservableProperty]
+        public partial string KeysFolderPath { get; set; }
+
+        [RelayCommand]
+        private static async Task Browse(TextBox tb)
+        {
+            Optional<IStorageFolder> result = await RyujinxApp.MainWindow.ViewModel.StorageProvider.OpenSingleFolderPickerAsync(new FolderPickerOpenOptions 
+            {
+                Title = LocaleManager.Instance[LocaleKeys.SetupWizardKeysPageFolderPopupTitle]
+            });
+
+            if (result.TryGet(out IStorageFolder keyFolder)) 
+            {
+                tb.Text = keyFolder.TryGetLocalPath();
+            }
+        }
+
+        private Result InstallKeys(string directory)
+        {
+            try
+            {
+                string systemDirectory = AppDataManager.KeysDirPath;
+                if (AppDataManager.Mode == AppDataManager.LaunchMode.UserProfile &&
+                    Directory.Exists(AppDataManager.KeysDirPathUser))
+                {
+                    systemDirectory = AppDataManager.KeysDirPathUser;
+                }
+
+                Logger.Info?.Print(LogClass.Application, $"Installing keys from {directory}");
+
+                ContentManager.InstallKeys(directory, systemDirectory);
+
+                Notifications.NotifyInformation(
+                    title: LocaleManager.Instance[LocaleKeys.RyujinxInfo],
+                    text: LocaleManager.Instance[LocaleKeys.DialogKeysInstallerKeysInstallSuccessMessage]);
+            }
+            catch (InvalidFirmwarePackageException ifwpe)
+            {
+                Notifications.NotifyError(ifwpe.Message, waitingExit: true);
+                return Result.Failure(NoKeysFoundInFolder.Shared);
+            }
+            catch (MissingKeyException ex)
+            {
+                Notifications.NotifyError(ex.ToString(), waitingExit: true);
+                return Result.Failure(NoKeysFoundInFolder.Shared);
+            }
+            catch (Exception ex)
+            {
+                string message = ex.Message;
+                if (ex is FormatException)
+                {
+                    message = LocaleManager.Instance.UpdateAndGetDynamicValue(
+                        LocaleKeys.DialogKeysInstallerKeysNotFoundErrorMessage, directory);
+                }
+
+                Notifications.NotifyError(message, waitingExit: true);
+
+                return Result.Failure(new MessageError(message));
+            }
+            finally
+            {
+                RyujinxApp.MainWindow.VirtualFileSystem.ReloadKeySet();
+            }
+
+            return Result.Success;
+        }
+    }
+
+    public struct NoKeysFoundInFolder : IErrorState
+    {
+        public static readonly NoKeysFoundInFolder Shared = new();
+    }
+}