7 files declare their use of AttributeInterface

AttributeClassDiscovery.php in core/lib/Drupal/Core/Plugin/Discovery/AttributeClassDiscovery.php
AttributeClassDiscovery.php in core/lib/Drupal/Component/Plugin/Discovery/AttributeClassDiscovery.php
AttributeClassDiscoveryAutomatedProviders.php in core/modules/migrate/src/Plugin/Discovery/AttributeClassDiscoveryAutomatedProviders.php
AttributeDiscoveryWithAnnotationsAutomatedProviders.php in core/modules/migrate/src/Plugin/Discovery/AttributeDiscoveryWithAnnotationsAutomatedProviders.php
DefaultPluginManager.php in core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
MigratePluginManager.php in core/modules/migrate/src/Plugin/MigratePluginManager.php
MultipleProviderAttributeInterface.php in core/modules/migrate/src/Attribute/MultipleProviderAttributeInterface.php

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