8 files declare their use of StateInterface in Drupal 8

ContentModeration.php in core/modules/content_moderation/src/Plugin/WorkflowType/ContentModeration.php

ContentModerationState.php in core/modules/content_moderation/src/ContentModerationState.php

ContentModerationStateForm.php in core/modules/content_moderation/src/Form/ContentModerationStateForm.php

StateTransitionValidation.php in core/modules/content_moderation/src/StateTransitionValidation.php

StateTransitionValidationInterface.php in core/modules/content_moderation/src/StateTransitionValidationInterface.php

WorkflowStateAddForm.php in core/modules/workflows/src/Form/WorkflowStateAddForm.php

WorkflowStateEditForm.php in core/modules/workflows/src/Form/WorkflowStateEditForm.php

WorkflowTypeBase.php in core/modules/workflows/src/Plugin/WorkflowTypeBase.php