6 files declare their use of PageManagerContextEvent in Page Manager 8.4

CurrentUserContext.php in src/EventSubscriber/CurrentUserContext.php

LanguageInterfaceContext.php in src/EventSubscriber/LanguageInterfaceContext.php

Page.php in src/Entity/Page.php

PageContextTestBase.php in tests/src/Unit/PageContextTestBase.php

PageTest.php in tests/src/Unit/PageTest.php

RouteParamContext.php in src/EventSubscriber/RouteParamContext.php