Support deserializing string to numeric property

[MikeAlhayek]

Previously using Newtonsoft, we ere able to deserialize a string from a string to numeric. In other words the following two json worked

{"name":"One","value":"1","Weight":1}

{"name":"One","value":"1","Weight":"1"}

when deserializing to

public sealed class CustomListValueOption : ListValueOption
{
    public string Name { get; set; }

    public string Value { get; set; }

    public double? Weight { get; set; }
}

This no longer works after converting to using System Json Text.