6 files declare their use of RouteBuilderInterface in Drupal 8

EntityOperations.php in core/modules/content_moderation/src/EntityOperations.php

MediaConfigSubscriber.php in core/modules/media/src/EventSubscriber/MediaConfigSubscriber.php

NodeAdminRouteSubscriber.php in core/modules/node/src/EventSubscriber/NodeAdminRouteSubscriber.php

RestConfigSubscriber.php in core/modules/rest/src/EventSubscriber/RestConfigSubscriber.php

SystemConfigSubscriber.php in core/modules/system/src/SystemConfigSubscriber.php

ThemeInstaller.php in core/lib/Drupal/Core/Extension/ThemeInstaller.php