Issue #2190895 by frankcarey, tim.plunkett: Revamp vertical tabs to not save form values

core/lib/Drupal/Core/Form/FormState.php

core/lib/Drupal/Core/Form/FormStateInterface.php

core/lib/Drupal/Core/Render/Element/VerticalTabs.php

...odules/system/src/Tests/Form/ElementsVerticalTabsTest.php

core/modules/system/src/Tests/Form/StateValuesCleanTest.php

...s/form_test/src/Form/FormTestFormStateValuesCleanForm.php

...s/modules/form_test/src/Form/FormTestVerticalTabsForm.php

core/tests/Drupal/Tests/Core/Form/FormStateTest.php