Add scaled ComboBox to ControlCatalog.
Add scaled ComboBox to ControlCatalog.

To test #7147.

AvaloniaUI/Avalonia,AvaloniaUI/Avalonia,SuperJMN/Avalonia,SuperJMN/Avalonia,AvaloniaUI/Avalonia,SuperJMN/Avalonia,AvaloniaUI/Avalonia,AvaloniaUI/Avalonia,AvaloniaUI/Avalonia,grokys/Perspex,grokys/Perspex,SuperJMN/Avalonia,SuperJMN/Avalonia,SuperJMN/Avalonia,AvaloniaUI/Avalonia,SuperJMN/Avalonia