Add the notion of "Parent" to pocos

[ewoutkramer]

Or whatever is necessary to implement the new interface #2894.

[ewoutkramer]

We used this scratch code during our discussions:

interface IScopedNode
{
    string Name;

    IEnumerable<object> Children()
}


class Base : IScopedNode
{
    virtual IScopedNode.Children()
    {
        foreach(child c in ....)
        {
            c._parent = this;
            yield c;
        }
    }

    IScopedNode AsRootNode()
    
        this._parent = null;
        return (IScopedNode)this;
    } 

}


var p = new Patient() { .... };
var isn = p.AsScopedNode();
var namex = isn.Select("resolve()").First();

[ewoutkramer]

This is part of #2910, and I consider this design done.