UI: chore: remove direct static MainWindowViewModel reference

src/Ryujinx/UI/Models/SaveModel.cs

+using Gommon;
 using LibHac.Fs;
 using LibHac.Ncm;
 using Ryujinx.Ava.UI.ViewModels;
@@ -47,7 +48,7 @@ namespace Ryujinx.Ava.UI.Models
             TitleId = info.ProgramId;
             UserId = info.UserId;
 
-            var appData = MainWindow.MainWindowViewModel.Applications.FirstOrDefault(x => x.IdString.Equals(TitleIdString, StringComparison.OrdinalIgnoreCase));
+            var appData = RyujinxApp.MainWindow.ViewModel.Applications.FirstOrDefault(x => x.IdString.EqualsIgnoreCase(TitleIdString));
 
             InGameList = appData != null;
 

src/Ryujinx/UI/ViewModels/SettingsViewModel.cs

@@ -750,7 +750,7 @@ namespace Ryujinx.Ava.UI.ViewModels
             config.ToFileFormat().SaveConfig(Program.ConfigurationPath);
 
             MainWindow.UpdateGraphicsConfig();
-            MainWindow.MainWindowViewModel.VSyncModeSettingChanged();
+            RyujinxApp.MainWindow.ViewModel.VSyncModeSettingChanged();
 
             SaveSettingsEvent?.Invoke();
 

src/Ryujinx/UI/Windows/MainWindow.axaml.cs

@@ -39,8 +39,6 @@ namespace Ryujinx.Ava.UI.Windows
 {
     public partial class MainWindow : StyleableAppWindow
     {
-        internal static MainWindowViewModel MainWindowViewModel { get; private set; }
-        
         public MainWindowViewModel ViewModel { get; }
 
         internal readonly AvaHostUIHandler UiHandler;
@@ -76,7 +74,7 @@ namespace Ryujinx.Ava.UI.Windows
 
         public MainWindow()
         {
-            DataContext = ViewModel = MainWindowViewModel = new MainWindowViewModel
+            DataContext = ViewModel = new MainWindowViewModel
             {
                 Window = this
             };