Issue #2919482: clean code - better use of WorkflowInterface declarations

src/Entity/Workflow.php

src/Entity/WorkflowManager.php

src/Entity/WorkflowState.php

src/Form/WorkflowTypeForm.php

src/Plugin/Action/WorkflowStateActionBase.php

src/Plugin/Field/FieldWidget/WorkflowDefaultWidget.php

src/WorkflowListBuilder.php

src/WorkflowTypeAttributeTrait.php

workflow.api.php

workflow.module