Update the MVVM Template to contain one Binding

[timunie]

Oh, wow. I already read about RaiseAndSetIfChanged but it was not visible in my scope. So I thought it was some old technique because the example here looks way more complicated:
https://www.reactiveui.net/docs/handbook/data-binding/avalonia

I did not expect it to be just an extension method. This is why I hate extension methods 😑
Maybe the visual studio template should include such basic binding as an example.
There current example only has a one way binding.

Originally posted by @ckorn in AvaloniaUI/Avalonia#8116 (comment)

[maxkatz6]

Also https://github.com/AvaloniaUI/AvaloniaVS can be updated as well (can't duplicate issue while transferring)