19 files declare their use of ClassResolverInterface in Drupal 9

ConstraintValidatorFactory.php in core/lib/Drupal/Core/Validation/ConstraintValidatorFactory.php

ContextDefinitionIsSatisfiedTest.php in core/tests/Drupal/Tests/Core/Plugin/Context/ContextDefinitionIsSatisfiedTest.php

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

Contains \Drupal\Tests\Core\Plugin\ContextHandlerTest.

ControllerResolver.php in core/lib/Drupal/Core/Controller/ControllerResolver.php

DrupalTest.php in core/tests/Drupal/Tests/Core/DrupalTest.php

EntityContextDefinitionIsSatisfiedTest.php in core/tests/Drupal/Tests/Core/Plugin/Context/EntityContextDefinitionIsSatisfiedTest.php

EntityResolverManager.php in core/lib/Drupal/Core/Entity/EntityResolverManager.php

EntityTypeManager.php in core/lib/Drupal/Core/Entity/EntityTypeManager.php

FormBuilder.php in core/lib/Drupal/Core/Form/FormBuilder.php

HtmlFormController.php in core/lib/Drupal/Core/Controller/HtmlFormController.php

MainContentViewSubscriber.php in core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php

MenuLinkEditForm.php in core/modules/menu_ui/src/Form/MenuLinkEditForm.php

PluginFormFactory.php in core/lib/Drupal/Core/Plugin/PluginFormFactory.php

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

ThemeNegotiator.php in core/lib/Drupal/Core/Theme/ThemeNegotiator.php

TypedConfigManager.php in core/lib/Drupal/Core/Config/TypedConfigManager.php

TypedDataManager.php in core/lib/Drupal/Core/TypedData/TypedDataManager.php

ViewsForm.php in core/modules/views/src/Form/ViewsForm.php

WorkspaceManager.php in core/modules/workspaces/src/WorkspaceManager.php