[PHPExcel] to PHPSpreadSheet

[TomasVotruba]

See https://phpspreadsheet.readthedocs.io/en/latest/topics/migration-from-PHPExcel/

Tool: https://github.com/PHPOffice/PhpSpreadsheet/blob/87f71e1930b497b36e3b9b1522117dfa87096d2b/src/PhpSpreadsheet/Helper/Migrator.php

Docs: https://github.com/PHPOffice/PhpSpreadsheet/blob/master/docs/topics/migration-from-PHPExcel.md

Test case: https://github.com/PHPOffice/PhpSpreadsheet/blob/master/tests/PhpSpreadsheetTests/Helper/MigratorTest.php