7 files declare their use of AlterableInterface

database_test.module in drupal/core/modules/system/tests/modules/database_test/database_test.module
entity_reference.module in drupal/core/modules/entity_reference/entity_reference.module
Provides a field that can reference other entities.
GroupwiseMax.php in drupal/core/modules/views/lib/Drupal/views/Plugin/views/relationship/GroupwiseMax.php
Definition of Drupal\views\Plugin\views\relationship\GroupwiseMax.
node.module in drupal/core/modules/node/node.module
The core module that allows content to be submitted to the site.
QueryInterface.php in drupal/core/lib/Drupal/Core/Entity/Query/QueryInterface.php
Contains \Drupal\Core\Entity\QueryInterface.
SelectionBase.php in drupal/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/entity_reference/selection/SelectionBase.php
Contains \Drupal\entity_reference\Plugin\entity_reference\selection\SelectionBase.
views.module in drupal/core/modules/views/views.module
Primarily Drupal hooks and global API functions to manipulate views.