layout: Take sticky offsets into account for offset queries (#39385)

`offsetLeft` and `offsetTop` were ignoring that sticky positioned boxes
can be shifted out of their normal position.

Testing: Various test improvements.

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

components/layout/fragment_tree/box_fragment.rs

@@ -569,4 +569,8 @@ impl BoxFragment {
             _ => false,
         }
     }
+
+    pub(crate) fn spatial_tree_node(&self) -> Option<ScrollTreeNodeId> {
+        *self.spatial_tree_node.borrow()
+    }
 }