make DataTables:getCellContent() a public function again (#919)

Refs: #918

Author: simontaurus

formats/datatables/DataTables.php

@@ -878,7 +878,7 @@ private function getResultJson( QueryResult $res, int $outputMode ): array {
 	/**
 	 * @see SMW\Query\ResultPrinters\TableResultPrinter
 	 */
-	private function getCellContent(
+	public function getCellContent(
 		string $label,
 		array $dataValues,
 		int $outputMode,