Don't rely on the removed "role=row" and "role=columnheader" attributes

[gino0631]

The datatable styling relies on "role=row" and "role=columnheader" attributes, e.g.: https://github.com/adminfaces/admin-theme/blob/f857cb4dc01a90fdca5c90ce9df2755ea1c81eb9/src/main/resources/less/primefaces-admin/components/datatable.less#L86

Unfortunately, these attributes were removed in PrimeFaces 12 (primefaces/primefaces#9261), so the corresponding CSS properties no longer get applied.