10 files declare their use of EntityWithPluginCollectionInterface in Zircon Profile 8

Action.php in core/modules/system/src/Entity/Action.php

Contains \Drupal\system\Entity\Action.

Block.php in core/modules/block/src/Entity/Block.php

Contains \Drupal\block\Entity\Block.

ConfigEntityBase.php in core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php

Contains \Drupal\Core\Config\Entity\ConfigEntityBase.

ConfigEntityBaseWithPluginCollections.php in core/tests/Drupal/Tests/Core/Config/Entity/Fixtures/ConfigEntityBaseWithPluginCollections.php

Contains \Drupal\Tests\Core\Config\Entity\Fixtures\ConfigEntityBaseWithPluginCollections.

ConfigEntityImportTest.php in core/modules/system/src/Tests/Entity/ConfigEntityImportTest.php

Contains \Drupal\system\Tests\Entity\ConfigEntityImportTest.

EntityDisplayFormBase.php in core/modules/field_ui/src/Form/EntityDisplayFormBase.php

Contains \Drupal\field_ui\Form\EntityDisplayFormBase.

EntityDisplayInterface.php in core/lib/Drupal/Core/Entity/Display/EntityDisplayInterface.php

Contains \Drupal\Core\Entity\Display\EntityDisplayInterface.

FilterFormat.php in core/modules/filter/src/Entity/FilterFormat.php

Contains \Drupal\filter\Entity\FilterFormat.

ImageStyle.php in core/modules/image/src/Entity/ImageStyle.php

Contains \Drupal\image\Entity\ImageStyle.

SearchPage.php in core/modules/search/src/Entity/SearchPage.php

Contains \Drupal\search\Entity\SearchPage.