Create single arity generic type formatter from JsonFormatterAttribute

[russcam]

This PR allows the construction of a closed generic type IJsonFormatter<T> from a JsonFormatterAttribute on a property of a generic type, where the property type is a generic parameter, and the IJsonFormatter<T> is an open generic type.

Consider

public class Foo<T>
{
    public T Bar { get; set; }
}

We may wish to define an IJsonFormatter<T> for property Bar. This commit allows the following

public class Foo<T>
{
    [JsonFormatter(typeof(BarFormatter<>)]
    public T Bar { get; set; }
}

without needing to introduce a formatter for Foo<T>