Initial work on a setup wizard

Setup wizard abstraction & architecture from TKMM

src/Ryujinx/UI/SetupWizard/Pages/SetupKeysPage.axaml

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+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:pages="clr-namespace:Ryujinx.UI.SetupWizard.Pages"
+             xmlns:markup="clr-namespace:Ryujinx.Ava.Common.Markup"
+             mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
+             x:Class="Ryujinx.UI.SetupWizard.Pages.SetupKeysPage"
+             x:DataType="pages:SetupKeysPageViewModel">
+    <StackPanel>
+        <TextBlock Text="{markup:Locale SetupWizardKeysPageDescription}" Margin="0,0,0,10"/>
+        <Grid ColumnDefinitions="*,Auto">
+            <TextBox Name="KeysFolderPathField" Text="{Binding KeysFolderPath}" IsReadOnly="True" />
+            <Button Grid.Column="1"
+                    Content="..."
+                    Command="{Binding BrowseCommand}"
+                    CommandParameter="{Binding #KeysFolderPathField}" 
+                    Margin="5,0,0,0"/>
+        </Grid>
+    </StackPanel>
+</UserControl>
+

src/Ryujinx/UI/SetupWizard/Pages/SetupKeysPage.axaml.cs

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+using Ryujinx.Ava.UI.Controls;
+
+namespace Ryujinx.UI.SetupWizard.Pages
+{
+    public partial class SetupKeysPage : RyujinxControl<SetupKeysPageViewModel>
+    {
+        public SetupKeysPage()
+        {
+            InitializeComponent();
+        }
+    }
+}
+

src/Ryujinx/UI/SetupWizard/Pages/SetupKeysPageViewModel.cs

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+using Avalonia.Controls;
+using Avalonia.Platform.Storage;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Ryujinx.Ava;
+using Ryujinx.Ava.Common.Locale;
+using Ryujinx.Ava.UI.ViewModels;
+using System.Threading.Tasks;
+
+namespace Ryujinx.UI.SetupWizard.Pages
+{
+    public partial class SetupKeysPageViewModel : BaseModel
+    {
+        [ObservableProperty]
+        public partial string? KeysFolderPath { get; set; }
+
+        [RelayCommand]
+        private static async Task Browse(TextBox tb)
+        {
+            var result = await RyujinxApp.MainWindow.ViewModel.StorageProvider.OpenFolderPickerAsync(new FolderPickerOpenOptions {
+                Title = LocaleManager.Instance[LocaleKeys.SetupWizardKeysPageFolderPopupTitle],
+                AllowMultiple = false
+            }) switch {
+                [var target] => target.TryGetLocalPath(),
+                _ => null
+            };
+
+            if (result is not null) 
+            {
+                tb.Text = result;
+            }
+        }
+    }
+}