Avalonia - Couple fixes and improvements to vulkan (#3483)

* drop split devices, rebase

* add fallback to opengl if vulkan is not available

* addressed review

* ensure present image references are incremented and decremented when necessary

* allow changing vsync for vulkan

* fix screenshot on avalonia vulkan

* save favorite when toggled

* improve sync between popups

* use separate devices for each new window

* fix crash when closing window

* addressed review

* don't create the main window with immediate mode

* change skia vk delegate to method

* update vulkan throwonerror

* addressed review

Ryujinx.Ava/Ui/Windows/MainWindow.axaml.cs

@@ -656,7 +656,12 @@ namespace Ryujinx.Ava.Ui.Windows
                 {
                     AppHost = null;
 
-                    Dispatcher.UIThread.Post(Close);
+                    Dispatcher.UIThread.Post(() =>
+                    {
+                        MainContent = null;
+
+                        Close();
+                    });
                 };
                 AppHost?.Stop();
 

Ryujinx.Ava/Ui/Windows/SettingsWindow.axaml

@@ -519,7 +519,7 @@
                                             HorizontalContentAlignment="Left"
                                             ToolTip.Tip="{locale:Locale SettingsTabGraphicsBackendTooltip}"
                                             SelectedIndex="{Binding GraphicsBackendIndex}">
-                                        <ComboBoxItem>
+                                        <ComboBoxItem IsVisible="{Binding IsVulkanAvailable}">
                                             <TextBlock Text="Vulkan" />
                                         </ComboBoxItem>
                                         <ComboBoxItem>