Small improvements for table border collapse (#33452)

We were only collapsing the borders from adjacent cells. This patch also
handles the borders from rows, row groups, columns, and column groups.
Additionally, it takes the border style into account in order to decide
which border wins.

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

components/layout_2020/style_ext.rs

@@ -16,7 +16,9 @@ use style::properties::ComputedValues;
 use style::servo::selector_parser::PseudoElement;
 use style::values::computed::basic_shape::ClipPath;
 use style::values::computed::image::Image as ComputedImageLayer;
-use style::values::computed::{AlignItems, LengthPercentage, NonNegativeLengthPercentage, Size};
+use style::values::computed::{
+    AlignItems, BorderStyle, LengthPercentage, NonNegativeLengthPercentage, Size,
+};
 use style::values::generics::box_::Perspective;
 use style::values::generics::length::MaxSize;
 use style::values::generics::position::{GenericAspectRatio, PreferredRatio};
@@ -250,6 +252,8 @@ pub(crate) trait ComputedValuesExt {
         &self,
         containing_block_writing_mode: WritingMode,
     ) -> LogicalSides<&LengthPercentage>;
+    fn border_style(&self, containing_block_writing_mode: WritingMode)
+        -> LogicalSides<BorderStyle>;
     fn border_width(&self, containing_block_writing_mode: WritingMode) -> LogicalSides<Au>;
     fn margin(
         &self,
@@ -553,6 +557,22 @@ impl ComputedValuesExt for ComputedValues {
         )
     }
 
+    fn border_style(
+        &self,
+        containing_block_writing_mode: WritingMode,
+    ) -> LogicalSides<BorderStyle> {
+        let border = self.get_border();
+        LogicalSides::from_physical(
+            &PhysicalSides::new(
+                border.border_top_style,
+                border.border_right_style,
+                border.border_bottom_style,
+                border.border_left_style,
+            ),
+            containing_block_writing_mode,
+        )
+    }
+
     fn border_width(&self, containing_block_writing_mode: WritingMode) -> LogicalSides<Au> {
         let border = self.get_border();
         LogicalSides::from_physical(