Reject unknown fields when converting from Struct to Object

This is mostly useful when a function loads its input from the
RunFunctionRequest. Crossplane isn't (yet) aware of input schema and
will send anything the user supplies.

Right now that could include extra unknown, misindented, or typod fields
and those will be silently ignored by the function. With this change in
place they will result in an error.

This code will also be used to load desired and observed resource state,
but it's unlikely for those to be invalid.

This is a small behavior change, but I feel okay with it. The new
behavior is safer, probably won't affect anyone, and we're pre 1.0.

crossplane-contrib/function-patch-and-transform#91 (comment)

Signed-off-by: Nic Cope <nicc@rk0n.org>

Author: negz

resource/resource.go

@@ -91,7 +91,7 @@ func AsObject(s *structpb.Struct, o runtime.Object) error {
 	if err != nil {
 		return errors.Wrapf(err, "cannot marshal %T to JSON", s)
 	}
-	return errors.Wrapf(json.Unmarshal(b, o), "cannot unmarshal JSON from %T into %T", s, o)
+	return errors.Wrapf(json.Unmarshal(b, o, json.RejectUnknownMembers(true)), "cannot unmarshal JSON from %T into %T", s, o)
 }
 
 // AsStruct gets the supplied struct from the supplied Kubernetes object.