10 files declare their use of DiscoveryTrait in Drupal 9

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

HelpTopicDiscovery.php in core/modules/help_topics/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

NoSourcePluginDecorator.php in core/modules/migrate/src/Plugin/NoSourcePluginDecorator.php

PluginManagerBase.php in core/lib/Drupal/Component/Plugin/PluginManagerBase.php

ProviderFilterDecorator.php in core/modules/migrate/src/Plugin/Discovery/ProviderFilterDecorator.php

YamlDiscovery.php in core/lib/Drupal/Core/Plugin/Discovery/YamlDiscovery.php