Stylet Avalonia

This is a proof of concept port of Stylet to Avalonia. The goal of this port was to get Conductors and Screens working in Avalonia as I much prefer that architecture over ReactiveUI.

See further discussion here: canton7/Stylet#342

This implementation depends on Avalonia, similarly to how Stylet depends on WPF. Additionally, this version depends on Microsoft.Toolkit.Mvvm. This allows for the removal of PropertyChangedBase and EventAggregator.

Working Stylet Features

• Conductors
• Screens
• BindableCollection
• Execute

Unsupported Features

I found a few unsupported features in Avalonia. I'm not too familiar with Avalonia yet, some of these can probably be worked around.

1. There is no Loaded and Unloaded events, so OnViewLoaded() does not work. See AvaloniaUI/Avalonia#7908. There is a workaround using events for attaching and detaching from the visual tree.

2. Avalonia windows do not allow the owner to be explicitly set.

3. Avalonia windows do not have Top and Left, so the start up location logic in WindowManager is disabled. Perhaps we need to listen to changes in BoundsProperty?