private static Stream<NewDocumentType.Name> toDocumentNameStream(Set<NewDocumentType> globallyDistributedDocuments) {
        return globallyDistributedDocuments.stream().map(NewDocumentType::getFullName);
    }
Performs the following validations:
 - Verify that all global documents have required redundancy
 - Verify that all referred documents are present in services.xml
 - Verify that all referred documents are global

@author bjorncs
config-model/src/main/java/com/yahoo/vespa/model/content/GlobalDistributionValidator.java