Avalonia: Another Cleanup (#3494)

* Avalonia: Another Cleanup

This PR is a cleanup to the avalonia code recently added:

- Some XAML file are autoformatted like a previous PR.
- Dlc is renamed to DownloadableContent (Locale exclude).
- DownloadableContentManagerWindow is a bit improved (Fixes #3491).
- Some nits here and there.

* Fix GTK

* Remove AttachDebugDevTools

* Fix last warning

* Fix JSON fields

Ryujinx.Ava/Ui/Windows/StyleableWindow.cs

@@ -2,7 +2,6 @@
 using Avalonia.Controls.Primitives;
 using Avalonia.Media.Imaging;
 using Avalonia.Platform;
-using FluentAvalonia.UI.Controls;
 using System;
 using System.IO;
 using System.Reflection;