15 files declare their use of PagerSelectExtender in Drupal 9

CommentStorage.php in core/modules/comment/src/CommentStorage.php

DatabaseTestController.php in core/modules/system/tests/modules/database_test/src/Controller/DatabaseTestController.php

DatabaseTestForm.php in core/modules/system/tests/modules/database_test/src/Form/DatabaseTestForm.php

DbLogController.php in core/modules/dblog/src/Controller/DbLogController.php

ForumManager.php in core/modules/forum/src/ForumManager.php

HelpSearch.php in core/modules/help_topics/src/Plugin/Search/HelpSearch.php

NodeSearch.php in core/modules/node/src/Plugin/Search/NodeSearch.php

PagerManager.php in core/lib/Drupal/Core/Pager/PagerManager.php

PagerSelectExtender.php in core/tests/fixtures/database_drivers/module/corefake/src/Driver/Database/corefakeWithAllCustomClasses/PagerSelectExtender.php

PagerTestController.php in core/modules/system/tests/modules/pager_test/src/Controller/PagerTestController.php

SelectComplexTest.php in core/tests/Drupal/KernelTests/Core/Database/SelectComplexTest.php

SelectPagerDefaultTest.php in core/modules/system/tests/src/Functional/Database/SelectPagerDefaultTest.php

StringDatabaseStorage.php in core/modules/locale/src/StringDatabaseStorage.php

TrackerController.php in core/modules/tracker/src/Controller/TrackerController.php

UserSearch.php in core/modules/user/src/Plugin/Search/UserSearch.php