22 files declare their use of ConfigEntityInterface

ActionConfigEntityInterface.php in drupal/core/modules/system/lib/Drupal/system/ActionConfigEntityInterface.php
Contains \Drupal\system\ActionConfigEntityInterface.
BlockInterface.php in drupal/core/modules/block/lib/Drupal/block/BlockInterface.php
Contains \Drupal\block\Plugin\Core\Entity\BlockInterface.
BreakpointGroupInterface.php in drupal/core/modules/breakpoint/lib/Drupal/breakpoint/BreakpointGroupInterface.php
Contains \Drupal\breakpoint\Plugin\Core\Entity\BreakpointGroupInterface.
BreakpointInterface.php in drupal/core/modules/breakpoint/lib/Drupal/breakpoint/BreakpointInterface.php
Contains \Drupal\breakpoint\Plugin\Core\Entity\BreakpointInterface.
CategoryInterface.php in drupal/core/modules/contact/lib/Drupal/contact/CategoryInterface.php
Contains \Drupal\contact\Plugin\Core\Entity\CategoryInterface.
ConfigTestInterface.php in drupal/core/modules/config/tests/config_test/lib/Drupal/config_test/ConfigTestInterface.php
Contains \Drupal\config_test\Plugin\Core\Entity\ConfigTestInterface.
CustomBlockTypeInterface.php in drupal/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockTypeInterface.php
Contains \Drupal\custom_block\Plugin\Core\Entity\CustomBlockTypeInterface.
DisplayInterface.php in drupal/core/modules/layout/lib/Drupal/layout/Config/DisplayInterface.php
Definition of Drupal\layout\Config\DisplayInterface
EditorInterface.php in drupal/core/modules/editor/lib/Drupal/editor/EditorInterface.php
Contains \Drupal\editor\Plugin\Core\Entity\EditPluginInterface.
EntityDisplayBaseInterface.php in drupal/core/modules/entity/lib/Drupal/entity/EntityDisplayBaseInterface.php
Contains \Drupal\entity\Plugin\Core\Entity\EntityDisplayBaseInterface.
EntityViewModeInterface.php in drupal/core/modules/entity/lib/Drupal/entity/EntityViewModeInterface.php
Contains \Drupal\entity\EntityViewModeInterface.
FieldInstanceInterface.php in drupal/core/modules/field/lib/Drupal/field/FieldInstanceInterface.php
Contains \Drupal\field\FieldInstanceInterface.
FieldInterface.php in drupal/core/modules/field/lib/Drupal/field/FieldInterface.php
Contains \Drupal\field\FieldInterface.
FilterFormatInterface.php in drupal/core/modules/filter/lib/Drupal/filter/FilterFormatInterface.php
Contains \Drupal\filter\Plugin\Core\Entity\FilterFormatInterface.
ImageStyleInterface.php in drupal/core/modules/image/lib/Drupal/image/ImageStyleInterface.php
Contains \Drupal\image\Plugin\Core\Entity\ImageStyleInterface.
MenuInterface.php in drupal/core/modules/system/lib/Drupal/system/MenuInterface.php
Contains \Drupal\system\Plugin\Core\Entity\MenuInterface.
PictureMappingInterface.php in drupal/core/modules/picture/lib/Drupal/picture/PictureMappingInterface.php
Contains \Drupal\picture\Plugin\Core\Entity\PictureMappingInterface.
RoleInterface.php in drupal/core/modules/user/lib/Drupal/user/RoleInterface.php
Contains \Drupal\user\Plugin\Core\Entity\RoleInterface.
ShortcutInterface.php in drupal/core/modules/shortcut/lib/Drupal/shortcut/ShortcutInterface.php
Contains \Drupal\shortcut\Plugin\Core\Entity\ShortcutInterface.
TourInterface.php in drupal/core/modules/tour/lib/Drupal/tour/TourInterface.php
Contains \Drupal\tour\Plugin\Core\Entity\TourInterface.
ViewStorageInterface.php in drupal/core/modules/views/lib/Drupal/views/ViewStorageInterface.php
Definition of Drupal\views\ViewStorageInterface.
VocabularyInterface.php in drupal/core/modules/taxonomy/lib/Drupal/taxonomy/VocabularyInterface.php
Contains \Drupal\taxonomy\Plugin\Core\Entity\VocabularyInterface.