28 files declare their use of Config

BlockTheme.php in core/modules/block/src/Plugin/migrate/process/BlockTheme.php
BlockThemeDeprecationTest.php in core/modules/block/tests/src/Unit/Plugin/migrate/process/BlockThemeDeprecationTest.php
CheckpointStorage.php in core/lib/Drupal/Core/Config/Checkpoint/CheckpointStorage.php
CheckpointStorageTest.php in core/tests/Drupal/Tests/Core/Config/Checkpoint/CheckpointStorageTest.php
ConfigCRUDTest.php in core/tests/Drupal/KernelTests/Core/Config/ConfigCRUDTest.php
ConfigEntityStorage.php in core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php
ConfigEntityStorageTest.php in core/tests/Drupal/Tests/Core/Config/Entity/ConfigEntityStorageTest.php
ConfigEventsTest.php in core/tests/Drupal/KernelTests/Core/Config/ConfigEventsTest.php
ConfigFactoryTest.php in core/tests/Drupal/Tests/Core/Config/ConfigFactoryTest.php
ConfigFormBase.php in core/lib/Drupal/Core/Form/ConfigFormBase.php
ConfigImportSubscriber.php in core/lib/Drupal/Core/EventSubscriber/ConfigImportSubscriber.php
ConfigTarget.php in core/lib/Drupal/Core/Form/ConfigTarget.php
ConfigTargetTest.php in core/tests/Drupal/Tests/Core/Form/ConfigTargetTest.php
ConfigTest.php in core/tests/Drupal/Tests/Core/Config/ConfigTest.php
ConfigTestStorage.php in core/modules/config/tests/config_test/src/ConfigTestStorage.php
ElementInterface.php in core/modules/config_translation/src/FormElement/ElementInterface.php
FieldConfigStorage.php in core/modules/field/src/FieldConfigStorage.php
FormElementBase.php in core/modules/config_translation/src/FormElement/FormElementBase.php
HelpSearch.php in core/modules/help/src/Plugin/Search/HelpSearch.php
ImportableEntityStorageInterface.php in core/lib/Drupal/Core/Config/Entity/ImportableEntityStorageInterface.php
ListElement.php in core/modules/config_translation/src/FormElement/ListElement.php
NodeSearch.php in core/modules/node/src/Plugin/Search/NodeSearch.php
PluralVariants.php in core/modules/config_translation/src/FormElement/PluralVariants.php
QueryFactory.php in core/lib/Drupal/Core/Config/Entity/Query/QueryFactory.php
QueryFactoryTest.php in core/tests/Drupal/Tests/Core/Config/Entity/Query/QueryFactoryTest.php
TestLocalActionWithConfig.php in core/modules/system/tests/modules/menu_test/src/Plugin/Menu/LocalAction/TestLocalActionWithConfig.php
theme.inc in core/includes/theme.inc
The theme system, which controls the output of Drupal.
UserUpdate7002.php in core/modules/user/src/Plugin/migrate/process/d6/UserUpdate7002.php

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