9 files declare their use of OptionsProviderInterface in Drupal 9

AllowedValuesConstraintValidator.php in core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/AllowedValuesConstraintValidator.php

BaseFieldDefinition.php in core/lib/Drupal/Core/Field/BaseFieldDefinition.php

BooleanItem.php in core/lib/Drupal/Core/Field/Plugin/Field/FieldType/BooleanItem.php

EntityReferenceItem.php in core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php

FieldStorageConfig.php in core/modules/field/src/Entity/FieldStorageConfig.php

FilterAPITest.php in core/modules/filter/tests/src/Kernel/FilterAPITest.php

FilterFormat.php in core/modules/filter/src/Plugin/DataType/FilterFormat.php

LanguageItem.php in core/lib/Drupal/Core/Field/Plugin/Field/FieldType/LanguageItem.php

ListItemBase.php in core/modules/options/src/Plugin/Field/FieldType/ListItemBase.php