ObjectTypeValidator should not reject unknown fields

As previously discussed on WFCORE-2249, ObjectTypeValidator is being more strict than our basic standard by rejecting unknown fields. When I did WFCORE-2249 I decided not to fix that. But now after working on some transformation stuff with complex attributes, I've changed my mind. If we don't relax this, transformers for complex attributes will have to remove even undefined fields from the attribute, which is fussy code.

Transformers will have to do that anyway for hosts running versions prior to when this is fix is implemented but fixing this will help reduce how much that is required.