(PUP-2891) Treat override of class as an error.

This makes an attempt to override a class parameter issue an
error from the runtime layer rather than expecting the underlying
3x implementation to do it when the left expression does not
result in a resource, or a resource that has 'class' as resource type.
Merge pull request #2845 from hlindberg/PUP-2891_override-class-parameters-error

(PUP-2891) Treat override of class as an error.