15 files declare their use of EntityFormDisplayInterface in Drupal 8

ContentEntityForm.php in core/lib/Drupal/Core/Entity/ContentEntityForm.php

ContentEntityFormInterface.php in core/lib/Drupal/Core/Entity/ContentEntityFormInterface.php

content_moderation.module in core/modules/content_moderation/content_moderation.module

Contains content_moderation.module.

EntityDisplayRepositoryTest.php in core/tests/Drupal/KernelTests/Core/Entity/EntityDisplayRepositoryTest.php

EntityFormDisplay.php in core/lib/Drupal/Core/Entity/Entity/EntityFormDisplay.php

EntityLegacyTest.php in core/tests/Drupal/KernelTests/Core/Entity/EntityLegacyTest.php

EntityManagerTest.php in core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php

layout_builder_test.module in core/modules/layout_builder/tests/modules/layout_builder_test/layout_builder_test.module

Provides hook implementations for Layout Builder tests.

MediaSourceBase.php in core/modules/media/src/MediaSourceBase.php

MediaSourceInterface.php in core/modules/media/src/MediaSourceInterface.php

MigrateFieldInstanceWidgetSettingsTest.php in core/modules/field/tests/src/Kernel/Migrate/d7/MigrateFieldInstanceWidgetSettingsTest.php

OEmbed.php in core/modules/media/src/Plugin/media/Source/OEmbed.php

system.module in core/modules/system/system.module

Configuration system that lets administrators modify the workings of the site.

TestDifferentDisplays.php in core/modules/media/tests/modules/media_test_source/src/Plugin/media/Source/TestDifferentDisplays.php

TestWithHiddenSourceField.php in core/modules/media/tests/modules/media_test_source/src/Plugin/media/Source/TestWithHiddenSourceField.php