Fix Designer parsing registries for disabled Modeler features

Reproduction steps:
1. In Modeler, create a Schema and add a String field to it.
2. Create a Page Provider and set a predicate to the schema field that was created in the previous step.
3. Delete the whole Schema created in step 1 (a validation error will show up to inform the user that the Page Provider created in step 2 is now referencing a non-existing schema).
4. Go back to the Page Provider and disable it.
5. Access Designer: it will fail to load because of the validation issues in the Page Provider, even though it has been disabled.

Expected behaviour: Designer should load a work normally, as if the Page Provider no longer exists (as long as it is disabled).

Note: Currently, the registries that are received in Designer don't have this sort of information about disabled features. This might not be super trivial to add, as Ricardo already tried it when having a quick look at NXS-5642.