layout: simplify CollapsedBorderLine (#35125)

This used to be a struct that had a list of `CollapsedBorder`s, and the
maximum border width among that list.

However, this cached maximum border width was only used when resolving
the borders of the table. Therefore, for all grid lines except the first
and last ones per axis, this data was useless.

Also, in order to address #35123 I plan to retroactively zero out some
collapsed borders, which could invalidate this cache.

So this patch just removes the field and turns `CollapsedBorderLine`
into an alias of `Vec<CollapsedBorder>`.

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

components/layout_2020/table/mod.rs

@@ -327,11 +327,7 @@ pub(crate) struct CollapsedBorder {
 }
 
 /// Represents a piecewise sequence of collapsed borders along a line.
-#[derive(Clone, Debug, Default)]
-pub(crate) struct CollapsedBorderLine {
-    max_width: Au,
-    pub list: Vec<CollapsedBorder>,
-}
+pub(crate) type CollapsedBorderLine = Vec<CollapsedBorder>;
 
 #[derive(Clone, Debug)]
 pub(crate) struct SpecificTableGridInfo {