7 files declare their use of LayoutInterface in Layout 8.2

BoundDisplayInterface.php in lib/Drupal/layout/Config/BoundDisplayInterface.php

Definition of Drupal\layout\Config\BoundDisplayInterface

Display.php in lib/Drupal/layout/Entity/Display.php

Definition of Drupal\layout\Entity\Display.

DisplayBase.php in lib/Drupal/layout/Config/DisplayBase.php

Definition of Drupal\layout\Config\DisplayBase.

DisplayInterface.php in lib/Drupal/layout/Config/DisplayInterface.php

Definition of Drupal\layout\Config\DisplayInterface

StaticLayout.php in lib/Drupal/layout/Plugin/Layout/StaticLayout.php

Contains \Drupal\layout\Plugin\Layout\StaticLayout.

UnboundDisplay.php in lib/Drupal/layout/Entity/UnboundDisplay.php

Definition of Drupal\layout\Entity\Display.

UnboundDisplayInterface.php in lib/Drupal/layout/Config/UnboundDisplayInterface.php

Definition of Drupal\layout\Config\UnboundDisplayInterface