Issue #1799040 by dawehner: Fixed groupwise max relationship.

lib/Drupal/views/Plugin/views/relationship/GroupwiseMax.php

...pal/views/Tests/Taxonomy/RelationshipNodeTermDataTest.php

...l/views/Tests/Taxonomy/RelationshipRepresentativeNode.php

lib/Drupal/views/Tests/Taxonomy/TaxonomyTestBase.php

...rupal/views/Tests/User/RelationshipRepresentativeNode.php

lib/Drupal/views/Tests/User/UserTestBase.php

modules/taxonomy.views.inc

modules/user.views.inc

...ews_test_config/config/views.view.test_groupwise_term.yml

...ews_test_config/config/views.view.test_groupwise_user.yml

...config/config/views.view.test_taxonomy_node_term_data.yml