Feature proposal: provide inverse of DTInterfaceInfo/Extends property

[jrdouceur]

This is a proposal for a reverse property companion to the Extends property, enabling top-to-bottom traversal of an Interface hierarchy. So, in addition to the current property:

public IReadOnlyList<DTInterfaceInfo> Extends { get; }

There would be a new property:

public IReadOnlyList<DTInterfaceInfo> ExtendedBy { get; }