23 files declare their use of PluginBase

BlockContentDeletionTest.php in core/modules/block_content/tests/src/Kernel/BlockContentDeletionTest.php
BlockContentDeriverTest.php in core/modules/block_content/tests/src/Kernel/BlockContentDeriverTest.php
ConfigurablePluginInterfaceTest.php in core/tests/Drupal/Tests/Component/Plugin/ConfigurablePluginInterfaceTest.php
ContentEntityTest.php in core/modules/migrate_drupal/tests/src/Kernel/Plugin/migrate/source/ContentEntityTest.php
ContextualLinkDefault.php in core/lib/Drupal/Core/Menu/ContextualLinkDefault.php
DefaultSingleLazyPluginCollectionTest.php in core/tests/Drupal/Tests/Core/Plugin/DefaultSingleLazyPluginCollectionTest.php
Editor.php in core/modules/editor/src/Plugin/InPlaceEditor/Editor.php
EntityReferenceTranslationDeriver.php in core/modules/migrate_drupal/src/Plugin/migrate/EntityReferenceTranslationDeriver.php
ExtraFieldBlockDeriver.php in core/modules/layout_builder/src/Plugin/Derivative/ExtraFieldBlockDeriver.php
FieldBlockDeriver.php in core/modules/layout_builder/src/Plugin/Derivative/FieldBlockDeriver.php
LayoutBuilderEntityViewDisplay.php in core/modules/layout_builder/src/Entity/LayoutBuilderEntityViewDisplay.php
Llama.php in core/modules/ckeditor/tests/modules/src/Plugin/CKEditorPlugin/Llama.php
LocalActionDefault.php in core/lib/Drupal/Core/Menu/LocalActionDefault.php
LocalTaskDefault.php in core/lib/Drupal/Core/Menu/LocalTaskDefault.php
MigrationPluginManager.php in core/modules/migrate/src/Plugin/MigrationPluginManager.php
MockLayoutBlock.php in core/modules/system/tests/modules/plugin_test/src/Plugin/plugin_test/mock_block/MockLayoutBlock.php
MockTestBlock.php in core/modules/system/tests/modules/plugin_test/src/Plugin/plugin_test/mock_block/MockTestBlock.php
MockUserLoginBlock.php in core/modules/system/tests/modules/plugin_test/src/Plugin/plugin_test/mock_block/MockUserLoginBlock.php
PluginBase.php in core/lib/Drupal/Core/Plugin/PluginBase.php
PluginWithFormsTraitTest.php in core/tests/Drupal/Tests/Core/Plugin/PluginWithFormsTraitTest.php
QueueWorkerBase.php in core/lib/Drupal/Core/Queue/QueueWorkerBase.php
TestConfigurablePlugin.php in core/tests/Drupal/Tests/Core/Plugin/Fixtures/TestConfigurablePlugin.php
WorkflowTypeBase.php in core/modules/workflows/src/Plugin/WorkflowTypeBase.php

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