Ava UI: Refactor async usage (#5516)

* Remove `async void`

* Async LoadApplications

* Formatting and such

* Remove async from InstallUpdate

* Update src/Ryujinx.Ava/UI/Controls/ApplicationContextMenu.axaml.cs

Co-authored-by: TSRBerry <20988865+TSRBerry@users.noreply.github.com>

* Cleanup LoadApplications()

* Cleanup

* Formatting

* Revert some stuff

* Cleanup

* Update src/Ryujinx.Ava/UI/ViewModels/MainWindowViewModel.cs

Co-authored-by: Ac_K <Acoustik666@gmail.com>

* Ack suggestions

* Whitespace

* Fix Peri suggestion

* Add missing trailing commas

* Remove redundant method override

* Remove Dispatcher.UIThread.InvokeAsync/Post where possible

---------

Co-authored-by: TSR Berry <20988865+TSRBerry@users.noreply.github.com>
Co-authored-by: Ac_K <Acoustik666@gmail.com>

src/Ryujinx.Ava/App.axaml.cs

@@ -104,7 +104,7 @@ namespace Ryujinx.Ava
                 {
                     "Light" => ThemeVariant.Light,
                     "Dark" => ThemeVariant.Dark,
-                    _ => ThemeVariant.Default
+                    _ => ThemeVariant.Default,
                 };
 
                 if (enableCustomTheme)