Auto generate ParameterValueConverter for assignable types

[ChebanovDD]

Will simplify the creation of BindingContextProvider by eliminating the need to write ParameterValueConverters for each ViewModel.

The following will allow to provide any ViewModel for child elements.

[UxmlElement]
public partial class CommonBindingContextProvider : BindingContextProvider<IBindingContext>
{
}

Related thread #43 (comment)