9 files declare their use of DiscoveryTrait

AnnotatedClassDiscovery.php in core/lib/Drupal/Component/Annotation/Plugin/Discovery/AnnotatedClassDiscovery.php
AnnotationBridgeDecorator.php in core/lib/Drupal/Component/Annotation/Plugin/Discovery/AnnotationBridgeDecorator.php
ConfigSchemaDiscovery.php in core/lib/Drupal/Core/Config/Schema/ConfigSchemaDiscovery.php
DiscoveryTraitTest.php in core/tests/Drupal/Tests/Component/Plugin/Discovery/DiscoveryTraitTest.php
HelpTopicDiscovery.php in core/modules/help/src/HelpTopicDiscovery.php
HookDiscovery.php in core/lib/Drupal/Core/Plugin/Discovery/HookDiscovery.php
InfoHookDecorator.php in core/lib/Drupal/Core/Plugin/Discovery/InfoHookDecorator.php
PluginManagerBase.php in core/lib/Drupal/Component/Plugin/PluginManagerBase.php
YamlDiscovery.php in core/lib/Drupal/Core/Plugin/Discovery/YamlDiscovery.php

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