GraphQL compose viewfield integration

Testing instructions:

1. Add a custom field to any entity type
2. Make sure you have at least 1 view with a graphql display type
3. Add a subfield of type 'viewfield' and any other subfields you like
4. Configure the widget viewfield subfield options to enable any views with graphql display types.
5. Optionally - configure the custom field to allow 1 or unlimited values.
6. Create the entity with attached custom field
7. Test the advanced options in the viewfield subfield: arguments (tokens are supported) & items to display
8. Test output in graphql explorer