6 files declare their use of FieldStorageDefinition

EntityDefinitionTestTrait.php in core/modules/system/tests/src/Functional/Entity/Traits/EntityDefinitionTestTrait.php
EntityDefinitionUpdateTest.php in core/tests/Drupal/KernelTests/Core/Entity/EntityDefinitionUpdateTest.php
EntitySchemaTestHooks.php in core/modules/system/tests/modules/entity_schema_test/src/Hook/EntitySchemaTestHooks.php
EntityTestBaseFieldDisplay.php in core/modules/system/tests/modules/entity_test/src/Entity/EntityTestBaseFieldDisplay.php
EntityTestComputedBundleField.php in core/modules/system/tests/modules/entity_test/src/Entity/EntityTestComputedBundleField.php
entity_schema_test.module in core/modules/system/tests/modules/entity_schema_test/entity_schema_test.module

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