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/Fw/SetupFirmwarePageContext.cs

@@ -0,0 +1,117 @@
+using Avalonia.Controls;
+using Avalonia.Platform.Storage;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Gommon;
+using Ryujinx.Ava.Common.Locale;
+using Ryujinx.Ava.Utilities;
+using Ryujinx.Common.Configuration;
+using Ryujinx.HLE.FileSystem;
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Threading.Tasks;
+
+namespace Ryujinx.Ava.UI.SetupWizard.Pages
+{
+    public partial class SetupFirmwarePageContext : SetupWizardPageContext
+    {
+        [ObservableProperty]
+        public partial string FirmwareSourcePath { get; set; }
+
+        [RelayCommand]
+        private static async Task BrowseFile(TextBox tb)
+        {
+            Optional<IStorageFile> result = await RyujinxApp.MainWindow.ViewModel.StorageProvider.OpenSingleFilePickerAsync(new FilePickerOpenOptions
+            {
+                Title = LocaleManager.Instance[LocaleKeys.SetupWizardFirmwarePageFilePopupTitle],
+                FileTypeFilter = new List<FilePickerFileType>
+                {
+                    new(LocaleManager.Instance[LocaleKeys.FileDialogAllTypes])
+                    {
+                        Patterns = ["*.xci", "*.zip"],
+                        AppleUniformTypeIdentifiers = ["com.ryujinx.xci", "public.zip-archive"],
+                        MimeTypes = ["application/x-nx-xci", "application/zip"],
+                    },
+                    new("XCI")
+                    {
+                        Patterns = ["*.xci"],
+                        AppleUniformTypeIdentifiers = ["com.ryujinx.xci"],
+                        MimeTypes = ["application/x-nx-xci"],
+                    },
+                    new("ZIP")
+                    {
+                        Patterns = ["*.zip"],
+                        AppleUniformTypeIdentifiers = ["public.zip-archive"],
+                        MimeTypes = ["application/zip"],
+                    }
+                }
+            });
+
+            if (result.TryGet(out IStorageFile firmwareFile)) 
+            {
+                tb.Text = firmwareFile.TryGetLocalPath();
+            }
+        }
+
+        [RelayCommand]
+        private static async Task BrowseFolder(TextBox tb)
+        {
+            Optional<IStorageFolder> result = await RyujinxApp.MainWindow.ViewModel.StorageProvider.OpenSingleFolderPickerAsync(new FolderPickerOpenOptions 
+            {
+                Title = LocaleManager.Instance[LocaleKeys.SetupWizardFirmwarePageFolderPopupTitle]
+            });
+
+            if (result.TryGet(out IStorageFolder firmwareFolder)) 
+            {
+                tb.Text = firmwareFolder.TryGetLocalPath();
+            }
+        }
+
+        public override Result CompleteStep()
+        {
+            if (!Directory.Exists(FirmwareSourcePath))
+                return Result.Fail;
+
+            try
+            {
+                RyujinxApp.MainWindow.ContentManager.InstallFirmware(FirmwareSourcePath);
+                SystemVersion installedFwVer = RyujinxApp.MainWindow.ContentManager.GetCurrentFirmwareVersion();
+                if (installedFwVer != null)
+                {
+                    Notifications.NotifyInformation(
+                        "Firmware installed",
+                        $"Installed firmware version {installedFwVer.VersionString}."
+                    );
+                }
+                else
+                {
+                    Notifications.NotifyError(
+                        "Firmware not installed",
+                        $"It seems some error occurred when trying to install the firmware at path '{FirmwareSourcePath}'." +
+                        "\nDid that folder contain a firmware dump?"
+                    );
+                }
+                RyujinxApp.MainWindow.ViewModel.RefreshFirmwareStatus(installedFwVer, allowNullVersion: true);
+
+                // Purge Applet Cache.
+
+                DirectoryInfo miiEditorCacheFolder = new(
+                    Path.Combine(AppDataManager.GamesDirPath, "0100000000001009", "cache")
+                );
+
+                if (miiEditorCacheFolder.Exists)
+                {
+                    miiEditorCacheFolder.Delete(true);
+                }
+            }
+            catch (Exception e)
+            {
+                Notifications.NotifyError(e.Message, waitingExit: true);
+                return Result.Fail;
+            }
+
+            return Result.Success;
+        }
+    }
+}