LibWeb: Use IterationDecision in single level Node iteration methods

`Node::for_each_child()` and `Node::for_each_child_of_type()` callbacks
now return an `IterationDecision`, which allows us to break early if
required.

Userland/Libraries/LibWeb/Layout/Node.cpp

@@ -882,6 +882,7 @@ void NodeWithStyle::propagate_style_to_anonymous_wrappers()
             auto& child_computed_values = static_cast<CSS::MutableComputedValues&>(static_cast<CSS::ComputedValues&>(const_cast<CSS::ImmutableComputedValues&>(child.computed_values())));
             child_computed_values.inherit_from(computed_values());
         }
+        return IterationDecision::Continue;
     });
 }