6 files declare their use of SchemaProviderInterface in Schema 8

Caching.php in src/Plugin/Schema/Caching.php

Contains Drupal\schema\Plugin\Schema\Caching.

Config.php in src/Plugin/Schema/Config.php

Contains Drupal\schema\Plugin\Schema\Config.

Entity.php in src/Plugin/Schema/Entity.php

Contains Drupal\schema\Plugin\Schema\Entity.

Menu.php in src/Plugin/Schema/Menu.php

Contains Drupal\schema\Plugin\Schema\Menu.

schema.module in ./schema.module

The Schema module provides functionality built on the Schema API.

System.php in src/Plugin/Schema/System.php

Contains Drupal\schema\Plugin\Schema\System.