My recent decorator improvements turned @webapi_response_errors into a

pass-through decorator, updating the decorated function and returning it

directly instead of wrapping it.
This ended up breaking the case where decorators may stack without

another webapi decorator in-between them.
This change switches it back to returning a proper decorator function

that merges in properties. We could still go with a pass-through

approach and handle the merging within @webapi_response_errors, but it

seems best for now just to keep the logic as it was.

All unit tests pass.