rollup of 9327467a and b75bf09a

it seems both xls & xlsx export suffer from problems with multiple row heights
repeated ( if those rows are empty )

better default row detection ( associated with fdo#55621 )

previous patch associated with fdo#55621 compared single instances of row
heights to determine the default height, it didn't take into account though
repeated rows. Additionally the limit of rows heights ( where rows were empty )
considered when exporting xlsx was the old 65535 limit.

Change-Id: I3ed68a81517a3e55d1de1954fcb99e7cb39be337
Reviewed-on: https://gerrit.libreoffice.org/2004Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>