7 files declare their use of PluginInspectionInterface

CKEditorPluginInterface.php in drupal/core/modules/ckeditor/lib/Drupal/ckeditor/CKEditorPluginInterface.php
Contains \Drupal\ckeditor\CKEditorPluginInterface.
EditorPluginInterface.php in drupal/core/modules/editor/lib/Drupal/editor/Plugin/EditorPluginInterface.php
Contains \Drupal\editor\Plugin\EditPluginInterface.
EditPluginInterface.php in drupal/core/modules/edit/lib/Drupal/edit/EditPluginInterface.php
Contains \Drupal\edit\EditPluginInterface.
LayoutInterface.php in drupal/core/modules/layout/lib/Drupal/layout/Plugin/LayoutInterface.php
Definition of Drupal\layout\Plugin\LayoutInterface.
PluginInterface.php in drupal/core/modules/views/lib/Drupal/views/Plugin/views/PluginInterface.php
Definition of Drupal\views\Plugin\PluginInterface.
PluginSettingsInterface.php in drupal/core/modules/field/lib/Drupal/field/Plugin/PluginSettingsInterface.php
Definition of Drupal\field\Plugin\PluginSettingsInterface.
ResourceInterface.php in drupal/core/modules/rest/lib/Drupal/rest/Plugin/ResourceInterface.php
Contains \Drupal\rest\Plugin\ResourceInterface.