6 files declare their use of DataTypeHelperInterface in Search API 8

FieldsHelperTest.php in tests/src/Unit/FieldsHelperTest.php

FieldsProcessorPluginBase.php in src/Processor/FieldsProcessorPluginBase.php

Highlight.php in src/Plugin/search_api/processor/Highlight.php

HtmlFilter.php in src/Plugin/search_api/processor/HtmlFilter.php

IndexAddFieldsForm.php in src/Form/IndexAddFieldsForm.php

IndexFieldsForm.php in src/Form/IndexFieldsForm.php