fix ra-data-graphql-simple response parser for embedded arrays and objects

[djhi]

Problem

When a record has embedded arrays or objects that are not references, ra-data-graphql-simple still generates fields to handle references for them. This leads to invalid payloads sent to the backend when updating for instance

Solution

Check that embedded arrays and objects have identifiers before generating the field required for references. This is still not perfect but ra-data-graphql-simple shouldn't be used for real applications anyway