We were previously splitting collapsed borders into two halves, and then
paint each one as part of the corresponding cell. This looked wrong when
the border style wasn't solid, or when a cell spanned multiple tracks
and the border wasn't the same for all of them.
Now the borders of a table wrapper, table grid or table cell aren't
painted in collapsed borders mode. Instead, the resulting collapsed
borders are painted on their own.
Signed-off-by: Oriol Brufau <obrufau@igalia.com>
