9 string references to 'FieldMigration' in Drupal 8

d6_field.yml in core/modules/field/migrations/d6_field.yml

core/modules/field/migrations/d6_field.yml

d6_field_formatter_settings.yml in core/modules/field/migrations/d6_field_formatter_settings.yml

core/modules/field/migrations/d6_field_formatter_settings.yml

d6_field_instance.yml in core/modules/field/migrations/d6_field_instance.yml

core/modules/field/migrations/d6_field_instance.yml

d6_field_instance_widget_settings.yml in core/modules/field/migrations/d6_field_instance_widget_settings.yml

core/modules/field/migrations/d6_field_instance_widget_settings.yml

d7_field.yml in core/modules/field/migrations/d7_field.yml

core/modules/field/migrations/d7_field.yml

d7_field_formatter_settings.yml in core/modules/field/migrations/d7_field_formatter_settings.yml

core/modules/field/migrations/d7_field_formatter_settings.yml

d7_field_instance.yml in core/modules/field/migrations/d7_field_instance.yml

core/modules/field/migrations/d7_field_instance.yml

d7_field_instance_label_description_translation.yml in core/modules/config_translation/migrations/d7_field_instance_label_description_translation.yml

core/modules/config_translation/migrations/d7_field_instance_label_description_translation.yml

d7_field_instance_widget_settings.yml in core/modules/field/migrations/d7_field_instance_widget_settings.yml

core/modules/field/migrations/d7_field_instance_widget_settings.yml