Add support for managed dialogs

[Sawa121212]

Avalonia provides managed dialogs.

After opening UseManagedSystemDialogs, OpenFileDialog opens abnormally. Add support for managed dialogs.

How to test:

1. Add the UseManagedSystemDialogs() configuration to AppBuilder
2. Test on dialog windows
   Example of calling a window:

private async Task OnImportPicture()
{
    if (Application.Current?.ApplicationLifetime is not IClassicDesktopStyleApplicationLifetime desktop ||
        desktop.MainWindow?.StorageProvider is not { } provider)
    {
        throw new NullReferenceException("Missing StorageProvider instance.");
    }

    IReadOnlyList<IStorageFile> files = await provider.OpenFilePickerAsync(new FilePickerOpenOptions
    {
        Title = "Choose File",
        AllowMultiple = false
    }).ConfigureAwait(true);

    if (files.Count >= 1)
    {
        string filePath = files[0].TryGetLocalPath();
        if (File.Exists(filePath))
        {
            Picture = filePath;
        }
    }
}