layout: Add a new FragmentTree pass to calculate containing block rectangles (#36629)

When doing any kind of query, up until now, containing block rectangles
were calculated by walking the `FragmentTree` until the node being
queried was found. In order to make possible answering queries without
walking the `FragmentTree`, `Fragment`s need to cache their cumulative
containing block rectangles.

This change adds a new `FragmentTree` pass (during construction) that
takes care of calculating and caching these values. The new cached value
is used during resolved style queries and also scrolling area queries
(with the idea that all queries will eventually use them).

In addition, extra `FragmentTree` walks used for cancelling animations
for elements no longer in the `FragmentTree` are integrated into this
new traversal.

Testing: Covered by existing WPT tests.

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

components/layout/flow/root.rs

@@ -428,13 +428,14 @@ impl BoxTree {
                 acc.union(&child_overflow)
             });
 
-        FragmentTree {
+        FragmentTree::new(
+            layout_context,
             root_fragments,
             scrollable_overflow,
-            initial_containing_block: physical_containing_block,
-            canvas_background: self.canvas_background.clone(),
-            viewport_scroll_sensitivity: self.viewport_scroll_sensitivity,
-        }
+            physical_containing_block,
+            self.canvas_background.clone(),
+            self.viewport_scroll_sensitivity,
+        )
     }
 }