layout: Improve painting of collapsed borders in table layout (#34933)

This is still not the right approach, because we are not painting
collapsed borders as a single thing. Instead, we are splitting them
into two halves and paint each half on a different cell. This only
looks good for solid borders.

Signed-off-by: Oriol Brufau <obrufau@igalia.com>

components/layout_2020/fragment_tree/box_fragment.rs

@@ -20,6 +20,7 @@ use crate::geom::{
     AuOrAuto, LengthPercentageOrAuto, PhysicalPoint, PhysicalRect, PhysicalSides, ToLogical,
 };
 use crate::style_ext::ComputedValuesExt;
+use crate::table::SpecificTableOrTableCellInfo;
 use crate::taffy::SpecificTaffyGridInfo;
 
 /// Describes how a [`BoxFragment`] paints its background.
@@ -43,6 +44,7 @@ pub(crate) struct ExtraBackground {
 #[derive(Clone, Debug)]
 pub(crate) enum SpecificLayoutInfo {
     Grid(Box<SpecificTaffyGridInfo>),
+    TableOrTableCell(Box<SpecificTableOrTableCellInfo>),
 }
 
 #[derive(Serialize)]