Some class files use the old standard of Definition of Drupal...
Standard now is Contains \Drupal...
Do just field_ui.
Here is a grep that shows the filenames that need updated:
lib/Drupal/field_ui/DisplayOverview.php: * Definition of Drupal\field_ui\DisplayOverview.
lib/Drupal/field_ui/FieldOverview.php: * Definition of Drupal\field_ui\FieldOverview.
lib/Drupal/field_ui/OverviewBase.php: * Definition of Drupal\field_ui\OverviewBase.
lib/Drupal/field_ui/Tests/FieldUiTestBase.php: * Definition of Drupal\field_ui\Tests\FieldUiTestBase.
lib/Drupal/field_ui/Tests/ManageDisplayTest.php: * Definition of Drupal\field_ui\Tests\ManageDisplayTest.
lib/Drupal/field_ui/Tests/ManageFieldsTest.php: * Definition of Drupal\field_ui\Tests\ManageFieldsTest.
Make the patch that updates just these files and just these lines to keep the patch reviewable.
User interface changes
Find the doc standards meta and link it here.