8 files declare their use of FieldDiscoveryInterface in Drupal 9

D6NodeDeriver.php in core/modules/node/src/Plugin/migrate/D6NodeDeriver.php

D7NodeDeriver.php in core/modules/node/src/Plugin/migrate/D7NodeDeriver.php

D7TaxonomyTermDeriver.php in core/modules/taxonomy/src/Plugin/migrate/D7TaxonomyTermDeriver.php

FieldDiscoveryTest.php in core/modules/migrate_drupal/tests/src/Unit/FieldDiscoveryTest.php

FieldDiscoveryTest.php in core/modules/migrate_drupal/tests/src/Kernel/d6/FieldDiscoveryTest.php

FieldDiscoveryTest.php in core/modules/migrate_drupal/tests/src/Kernel/d7/FieldDiscoveryTest.php

FieldDiscoveryTestTrait.php in core/modules/migrate_drupal/tests/src/Traits/FieldDiscoveryTestTrait.php

FieldMigration.php in core/modules/migrate_drupal/src/Plugin/migrate/FieldMigration.php