RadioButtonGroupView should default its SelectedItemProperty to TwoWay

[vchelaru]

Is your feature request related to a problem? Please describe. I often create RadioButtonGroupViews which are bound to a property on my ViewModel and I do a simple binding:

groupView.SetBinding(RadioButtonGroupView.SelectedItemProperty, "MyProperty");

This is similar to how to bind to other controls like Entry and Editor which can both display and receive input from the user.

However, unlike those controls, the RadioButtonGroupView defaults to OneWay binding, and I always have to spend a minute until I remember to set it to TwoWay.

Describe the solution you'd like I'd like the RadioButtonGroupView's SelectedItemProperty to default to TwoWay so that the code shown above will work.

Describe alternatives you've considered I've considered making my own class that inherits from RadioButtonGroupView but that's a lot of extra work, and I think most of the users of InputKit would benefit from this default.

Additional context Seems like this was an intentional design decision, but I'm not sure why. This thread mentions to explicitly set TwoWay:

https://github.com/enisn/Xamarin.Forms.InputKit/issues/14

Also, thanks so much for this awesome library!