7 files declare their use of DefaultSingleLazyPluginCollection in Drupal 8

ActionPluginCollection.php in core/lib/Drupal/Core/Action/ActionPluginCollection.php

BlockPluginCollection.php in core/modules/block/src/BlockPluginCollection.php

DefaultSingleLazyPluginCollectionTest.php in core/tests/Drupal/Tests/Core/Plugin/DefaultSingleLazyPluginCollectionTest.php

MediaType.php in core/modules/media/src/Entity/MediaType.php

RestResourceConfig.php in core/modules/rest/src/Entity/RestResourceConfig.php

SearchPluginCollection.php in core/modules/search/src/Plugin/SearchPluginCollection.php

Workflow.php in core/modules/workflows/src/Entity/Workflow.php