Fix data table editor for fields of schemas with different id and prefix

Steps to reproduce:

1. Create a schema with the id myschema and the prefix ms.
2. Add a multivalued String field to it, with the id strings.
3. Create a doctype with the id and label mydoctype.
4. Add myschema to mydoctype.
5. In Designer, scaffold the create layout for mydoctype.
6. Try to edit the nuxeo-data-table generated for the strings field. Notice that the table editor does not open and in the console it is logged "Cannot read property 'fields' of undefined".

If the prefix of the schema is changed to myschema and the create layout is re-scaffolded, everything works as expected. This can also be reproduced by scaffolding the create layout for the File doctype, drag and dropping the facetedTag:tags field and trying to edit the generated nuxeo-data-table element (because the prefix for this schema is actually nxtag).