Issue #3427999 by andypost, Ayesh, bbrala: [PHP 8.4] Fix implicitly nullable type declarations

core/lib/Drupal/Core/Database/StatementWrapperIterator.php

.../lib/Drupal/Core/DependencyInjection/ContainerBuilder.php

core/lib/Drupal/Core/Display/VariantBase.php

core/lib/Drupal/Core/Display/VariantInterface.php

core/lib/Drupal/Core/Entity/ContentEntityBase.php

core/lib/Drupal/Core/Entity/ContentEntityNullStorage.php

core/lib/Drupal/Core/Entity/ContentEntityStorageBase.php

core/lib/Drupal/Core/Entity/Controller/EntityController.php

core/lib/Drupal/Core/Entity/EntityAccessControlHandler.php

...rupal/Core/Entity/EntityAccessControlHandlerInterface.php

core/lib/Drupal/Core/Entity/EntityBase.php

.../lib/Drupal/Core/Entity/EntityConstraintViolationList.php

...al/Core/Entity/EntityConstraintViolationListInterface.php

.../lib/Drupal/Core/Entity/EntityDefinitionUpdateManager.php

...al/Core/Entity/EntityDefinitionUpdateManagerInterface.php

core/lib/Drupal/Core/Entity/EntityInterface.php

...ntity/EntityReferenceSelection/SelectionPluginManager.php

...ityReferenceSelection/SelectionPluginManagerInterface.php

core/lib/Drupal/Core/Entity/EntityRepository.php

core/lib/Drupal/Core/Entity/EntityRepositoryInterface.php