Query: improve exception message we throw when trying to use Include on a complex type

The expression 'x.BillingAddress' is invalid inside an 'Include' operation, since it does not represent a property access: 't => t.MyProperty'. To target navigations declared on derived types, use casting ('t => ((Derived)t).MyProperty') or the 'as' operator ('t => (t as Derived).MyProperty'). Collection navigation access can be filtered by composing Where, OrderBy(Descending), ThenBy(Descending), Skip or Take operations. For more information on including related data, see https://go.microsoft.com/fwlink/?LinkID=746393.

We should clarify that we mean *navigation* property access.