Problem/Motivation
In some cases I've wanted to sort on the vocabulary machine name. When the `vid` was added, the sort option was manually unset, perhaps because it's not possible to sort on the vocabulary Label using SQL.
https://www.drupal.org/project/drupal/issues/2320743#comment-9157907
Proposed resolution
There is not a compelling reason why we don't allow sorting on the raw machine name, however it should be labelled in such a way as to be clear that it is the raw machine name that is being sorted on.
API changes
Adding a $values parameter to TaxononomyTestTrait where there was none. See #12.