12 files declare their use of ResponsePolicyInterface in Drupal 9

ChainResponsePolicyTest.php in core/tests/Drupal/Tests/Core/PageCache/ChainResponsePolicyTest.php

DenyAdminRoutes.php in core/modules/dynamic_page_cache/src/PageCache/ResponsePolicy/DenyAdminRoutes.php

DenyNoCacheRoutes.php in core/lib/Drupal/Core/PageCache/ResponsePolicy/DenyNoCacheRoutes.php

DenyNodePreview.php in core/modules/node/src/PageCache/DenyNodePreview.php

DenyNodePreviewTest.php in core/modules/node/tests/src/Unit/PageCache/DenyNodePreviewTest.php

DenyPrivateImageStyleDownload.php in core/modules/image/src/PageCache/DenyPrivateImageStyleDownload.php

DenyPrivateImageStyleDownloadTest.php in core/modules/image/tests/src/Unit/PageCache/DenyPrivateImageStyleDownloadTest.php

DynamicPageCacheSubscriber.php in core/modules/dynamic_page_cache/src/EventSubscriber/DynamicPageCacheSubscriber.php

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

KillSwitch.php in core/lib/Drupal/Core/PageCache/ResponsePolicy/KillSwitch.php

NoServerError.php in core/lib/Drupal/Core/PageCache/ResponsePolicy/NoServerError.php

PageCache.php in core/modules/page_cache/src/StackMiddleware/PageCache.php