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/SetupWizardPage.Builder.cs

@@ -0,0 +1,65 @@
+using Avalonia;
+using Avalonia.Controls;
+using Ryujinx.Ava.Common.Locale;
+using Ryujinx.Ava.UI.Controls;
+
+namespace Ryujinx.Ava.UI.SetupWizard
+{
+    public partial class SetupWizardPage
+    {
+        public SetupWizardPage WithTitle(LocaleKeys title) => WithTitle(LocaleManager.Instance[title]);
+
+        public SetupWizardPage WithTitle(string title)
+        {
+            Title = title;
+            return this;
+        }
+
+        public SetupWizardPage WithContent(LocaleKeys content) => WithContent(LocaleManager.Instance[content]);
+
+        public SetupWizardPage WithContent(object? content)
+        {
+            if (content is StyledElement { Parent: ContentControl parent })
+            {
+                parent.Content = null;
+            }
+
+            Content = content;
+            return this;
+        }
+
+        public SetupWizardPage WithHelpContent(LocaleKeys content) =>
+            WithHelpContent(LocaleManager.Instance[content]);
+
+        public SetupWizardPage WithHelpContent(object? content)
+        {
+            HelpContent = content;
+            return this;
+        }
+
+        public SetupWizardPage WithContent<TControl>(object? context = null) where TControl : Control, new()
+        {
+            Content = new TControl { DataContext = context };
+
+            return this;
+        }
+
+        public SetupWizardPage WithContent<TControl, TViewModel>(out TViewModel boundViewModel)
+            where TControl : RyujinxControl<TViewModel>, new()
+            where TViewModel : SetupWizardPageContext, new()
+        {
+            boundViewModel = new() { Notifications = ownerWizard.NotificationHelper };
+
+            return WithContent<TControl>(boundViewModel);
+        }
+
+        public SetupWizardPage WithActionContent(LocaleKeys content) =>
+            WithActionContent(LocaleManager.Instance[content]);
+
+        public SetupWizardPage WithActionContent(object? content)
+        {
+            ActionContent = content;
+            return this;
+        }
+    }
+}