14 files declare their use of ConfigurablePluginInterface in Zircon Profile 8

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

Contains \Drupal\system\Entity\Action.

AggregatorPluginSettingsBase.php in core/modules/aggregator/src/Plugin/AggregatorPluginSettingsBase.php

Contains \Drupal\aggregator\Plugin\AggregatorPluginSettingsBase.

BlockPluginInterface.php in core/lib/Drupal/Core/Block/BlockPluginInterface.php

Contains \Drupal\Core\Block\BlockPluginInterface.

ConditionInterface.php in core/lib/Drupal/Core/Condition/ConditionInterface.php

Contains \Drupal\Core\Condition\ConditionInterface.

ConfigurableActionBase.php in core/lib/Drupal/Core/Action/ConfigurableActionBase.php

Contains \Drupal\Core\Action\ConfigurableActionBase.

ConfigurableSearchPluginInterface.php in core/modules/search/src/Plugin/ConfigurableSearchPluginInterface.php

Contains \Drupal\search\Plugin\ConfigurableSearchPluginInterface.

ContextAwarePluginBase.php in core/lib/Drupal/Core/Plugin/ContextAwarePluginBase.php

Contains \Drupal\Core\Plugin\ContextAwarePluginBase.

ContextHandlerTest.php in core/tests/Drupal/Tests/Core/Plugin/ContextHandlerTest.php

Contains \Drupal\Tests\Core\Plugin\ContextHandlerTest.

DefaultLazyPluginCollection.php in core/lib/Drupal/Core/Plugin/DefaultLazyPluginCollection.php

Contains \Drupal\Core\Plugin\DefaultLazyPluginCollection.

DefaultSingleLazyPluginCollection.php in core/lib/Drupal/Core/Plugin/DefaultSingleLazyPluginCollection.php

Contains \Drupal\Core\Plugin\DefaultSingleLazyPluginCollection.

FilterInterface.php in core/modules/filter/src/Plugin/FilterInterface.php

Contains \Drupal\filter\Plugin\FilterInterface.

ImageEffectInterface.php in core/modules/image/src/ImageEffectInterface.php

Contains \Drupal\image\ImageEffectInterface.

TestConfigurablePlugin.php in core/tests/Drupal/Tests/Core/Plugin/Fixtures/TestConfigurablePlugin.php

Contains \Drupal\Tests\Core\Plugin\Fixtures\TestConfigurablePlugin.

VariantInterface.php in core/lib/Drupal/Core/Display/VariantInterface.php

Contains \Drupal\Core\Display\VariantInterface.