layout: Store Fragment results in LayoutBoxBase and start using them for queries (#36583)

Start storing a link to laid-out `Fragment`s in `LayoutBoxBase`, so that
these are accessible for queries and eventually for incremental layout.
Some box tree data structures lacked a `LayoutBoxBase`, such as table
tracks and table track groups[^1].

In addition, start using these `Fragment`s for queries instead of
walking the entire `Fragment` tree. Currently, this isn't possible for
most queries as `Fragment`s do not cache their absolute offsets (which
are often necessary). This change uses the new box tree `Fragment`s for
most resolved style queries.

[^1]: Note that only rows and row groups store `Fragment`s as columsn
and
   colgroups do not produce any.

Testing: This is covered by existing tests.
Fixes: This is part of #36525.

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

components/layout_2020/flow/inline/inline_box.rs

@@ -73,6 +73,10 @@ impl InlineBoxes {
         self.inline_boxes.len()
     }
 
+    pub(super) fn iter(&self) -> impl Iterator<Item = &ArcRefCell<InlineBox>> {
+        self.inline_boxes.iter()
+    }
+
     pub(super) fn get(&self, identifier: &InlineBoxIdentifier) -> ArcRefCell<InlineBox> {
         self.inline_boxes[identifier.index_in_inline_boxes as usize].clone()
     }