script: Skip clearing subtree layout boxes of detached element when attaching shadow to it (#44052)

There is no layout boxes to clear in this case. For the example in
#43998,
this skips the traversal many times.

Testing: Should not change visible behaviour.
[Try](https://github.com/servo/servo/actions/runs/24131782865).

---------

Signed-off-by: Euclid Ye <yezhizhenjiakang@gmail.com>

components/script/dom/element/element.rs

@@ -699,8 +699,9 @@ impl Element {
         // non-shadow-tree children of `self` no longer have layout boxes as they are no
         // longer in the flat tree.
         let node = self.upcast::<Node>();
-        node.remove_layout_boxes_from_subtree();
-
+        if node.is_connected() {
+            node.remove_layout_boxes_from_subtree();
+        }
         // Step 6. Set shadow's delegates focus to delegatesFocus
         shadow_root.set_delegates_focus(delegates_focus);
 

components/script/dom/node/node.rs

@@ -365,7 +365,7 @@ impl Node {
     }
 
     /// Clear this [`Node`]'s layout data and also clear the layout data of all children.
-    /// Note that clears layout data from all non-flat tree descendants and flat tree
+    /// Note that this clears layout data from all non-flat tree descendants and flat tree
     /// descendants.
     pub(crate) fn remove_layout_boxes_from_subtree(&self) {
         for node in self.traverse_preorder(ShadowIncluding::Yes) {