10 files declare their use of PluginWithFormsInterface in Drupal 8

BlockBase.php in core/lib/Drupal/Core/Block/BlockBase.php

BlockEntitySettingTrayForm.php in core/modules/settings_tray/src/Block/BlockEntitySettingTrayForm.php

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

BlockPluginHasSettingsTrayFormAccessCheck.php in core/modules/settings_tray/src/Access/BlockPluginHasSettingsTrayFormAccessCheck.php

BlockPluginHasSettingsTrayFormAccessCheckTest.php in core/modules/settings_tray/tests/src/Unit/Access/BlockPluginHasSettingsTrayFormAccessCheckTest.php

ConfigureBlockFormBase.php in core/modules/layout_builder/src/Form/ConfigureBlockFormBase.php

ConfigureSectionForm.php in core/modules/layout_builder/src/Form/ConfigureSectionForm.php

PluginFormFactoryTest.php in core/tests/Drupal/Tests/Core/Plugin/PluginFormFactoryTest.php

PluginWithFormsTraitTest.php in core/tests/Drupal/Tests/Core/Plugin/PluginWithFormsTraitTest.php

WorkflowTypeInterface.php in core/modules/workflows/src/WorkflowTypeInterface.php