17 files declare their use of PageInterface in Page Manager 8

AccessConfigure.php in page_manager_ui/src/Form/AccessConfigure.php

Contains \Drupal\page_manager_ui\Form\AccessConfigure;

AccessDelete.php in page_manager_ui/src/Form/AccessDelete.php

Contains \Drupal\page_manager_ui\Form\AccessDelete.

Page.php in src/Entity/Page.php

Contains \Drupal\page_manager\Entity\Page.

PageAccessTest.php in tests/src/Unit/PageAccessTest.php

Contains \Drupal\Tests\page_manager\Unit\PageAccessTest.

PageBlockDisplayVariantTest.php in tests/src/Unit/PageBlockDisplayVariantTest.php

Contains \Drupal\Tests\page_manager\Unit\PageBlockDisplayVariantTest.

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

Contains \Drupal\Tests\page_manager\Unit\PageContextTestBase.

PageEditWizard.php in page_manager_ui/src/Wizard/PageEditWizard.php

Contains \Drupal\page_manager_ui\Wizard\PageEditWizard.

PageListBuilder.php in page_manager_ui/src/Entity/PageListBuilder.php

Contains \Drupal\page_manager_ui\Entity\PageListBuilder.

PageManagerContextEvent.php in src/Event/PageManagerContextEvent.php

Contains \Drupal\page_manager\Event\PageManagerContextEvent.

PageManagerController.php in page_manager_ui/src/Controller/PageManagerController.php

Contains \Drupal\page_manager_ui\Controller\PageManagerController.

PageManagerRoutes.php in src/Routing/PageManagerRoutes.php

Contains \Drupal\page_manager\Routing\PageManagerRoutes.

PageManagerRoutesTest.php in tests/src/Unit/PageManagerRoutesTest.php

Contains \Drupal\Tests\page_manager\Unit\PageManagerRoutesTest.

PageReorderVariantsForm.php in page_manager_ui/src/Form/PageReorderVariantsForm.php

Contains Drupal\page_manager_ui\Form\PageReorderVariantsForm.

PageVariant.php in src/Entity/PageVariant.php

Contains Drupal\page_manager\Entity\PageVariant.

PageVariantAddForm.php in page_manager_ui/src/Form/PageVariantAddForm.php

Contains Drupal\page_manager_ui\Form\PageVariantAddForm.

PageVariantTest.php in tests/src/Unit/PageVariantTest.php

Contains \Drupal\Tests\page_manager\Unit\PageVariantTest.

ParameterEditForm.php in page_manager_ui/src/Form/ParameterEditForm.php

Contains \Drupal\page_manager_ui\Form\ParameterEditForm.