Add generic resolve script service method to resolve an entity reference

It's possible to serialize an entity reference using withtype to have a full serialization containing the type, then it's possible to parse those using any resolver if we don't specify the type. However, we're missing the capability to parse those from a script as all the script services methods we have for resolving references are typed (e.g. resolveDocument): we'd need a generic resolve() method that would return an EntityReference.