layout: Move text decoration propagation to stacking context tree construction (#37069)

Text decorations have a special kind of propagation. Instead of
propating these during box tree construction, move propagation to
stacking context tree construction. This will allow for using a very
easy type of incremental layout when text decorations change. For
instance, when a link changes color during hovering over it, we can skip
all of box and fragment tree construction.

In addition, propagation works a bit better now and color and style
properly move down from their originating `Fragment`s.

This introduces three new failures, because now we are drawing the
text-decoration with the correct color in more places, which exposes an
issue we have with text-decorations not being drawn in relation to the
baseline (taking into account `vertical-align`).

Testing: There are tests for these changes.
Fixes #31736.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>

components/layout/taffy/mod.rs

@@ -36,8 +36,7 @@ impl TaffyContainer {
         contents: NonReplacedContents,
         propagated_data: PropagatedBoxTreeData,
     ) -> Self {
-        let mut builder =
-            ModernContainerBuilder::new(context, info, propagated_data.union(&info.style));
+        let mut builder = ModernContainerBuilder::new(context, info, propagated_data);
         contents.traverse(context, info, &mut builder);
         let items = builder.finish();