Also add the method sw_CompareCellsByRowFirst into unotbl.hxx so that
it can be used elsewhere, just like sw_CompareCellsByColFirst can.
Change-Id: I4a88455ba73356013f9f630d07610825568c263c
Reviewed-on: https://gerrit.libreoffice.org/25260Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: jan iversen <jani@documentfoundation.org>