Previously we moved the types into Distribution.PackageDescription.Types.
Now all the remaining utils have been removed from D.PackageDescription we
can move D.PackageDescription.Types back to D.PackageDescription. Also move
D.Configuration to be D.PackageDescription.Configuration and move the types
used for GenericPackageDescription into D.PackageDescription and move the
functions that convert GenericPackageDescription -> PackageDescription into
the D.PackageDescription.Configuration module.