Add super types Edm.AnyPath and Edm.AnyPropertyPath

The three types Edm.PropertyPath, Edm.NavigationPropertyPath, and Edm.AnnotationPath take valid path expressions that end in a structural property, a navigation property, or an annotation.

In some cases we don't need to restrict the last path segment, we just want to be sure that the path is valid in its context, so we don't want to use Edm.String.