27 files declare their use of FormBuilderInterface in Drupal 9

AjaxFormBlock.php in core/modules/system/tests/modules/ajax_forms_test/src/Plugin/Block/AjaxFormBlock.php

AreaDisplayLinkTest.php in core/modules/views/tests/src/Kernel/Handler/AreaDisplayLinkTest.php

BlockListBuilder.php in core/modules/block/src/BlockListBuilder.php

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

DisplayLink.php in core/modules/views/src/Plugin/views/area/DisplayLink.php

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

EntityOperations.php in core/modules/content_moderation/src/EntityOperations.php

FileUploadForm.php in core/modules/media_library/src/Form/FileUploadForm.php

FormAjaxSubscriber.php in core/lib/Drupal/Core/Form/EventSubscriber/FormAjaxSubscriber.php

FormAjaxSubscriberTest.php in core/tests/Drupal/Tests/Core/Form/EventSubscriber/FormAjaxSubscriberTest.php

FormBuilderTest.php in core/tests/Drupal/Tests/Core/Form/FormBuilderTest.php

Contains \Drupal\Tests\Core\Form\FormBuilderTest.

FormController.php in core/lib/Drupal/Core/Controller/FormController.php

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

HtmlFormController.php in core/lib/Drupal/Core/Controller/HtmlFormController.php

MediaLibrarySelectForm.php in core/modules/media_library/src/Plugin/views/field/MediaLibrarySelectForm.php

MediaLibraryUiBuilder.php in core/modules/media_library/src/MediaLibraryUiBuilder.php

OEmbedForm.php in core/modules/media_library/src/Form/OEmbedForm.php

PathAliasListBuilder.php in core/modules/path/src/PathAliasListBuilder.php

RedirectFormBlock.php in core/modules/system/tests/modules/form_test/src/Plugin/Block/RedirectFormBlock.php

RenderElement.php in core/lib/Drupal/Core/Render/Element/RenderElement.php

RenderElementTest.php in core/tests/Drupal/Tests/Core/Render/Element/RenderElementTest.php

SearchBlock.php in core/modules/search/src/Plugin/Block/SearchBlock.php

SystemController.php in core/modules/system/src/Controller/SystemController.php

TestFormApiFormBlock.php in core/modules/layout_builder/tests/modules/layout_builder_form_block_test/src/Plugin/Block/TestFormApiFormBlock.php

TimezoneTest.php in core/tests/Drupal/KernelTests/Core/Datetime/Element/TimezoneTest.php

ViewAjaxController.php in core/modules/views/src/Controller/ViewAjaxController.php

WorkspaceSwitcherBlock.php in core/modules/workspaces/src/Plugin/Block/WorkspaceSwitcherBlock.php