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/HTML/HTMLImageElement.cpp

@@ -864,6 +864,7 @@ static void update_the_source_set(DOM::Element& element)
         elements.clear();
         element.parent()->for_each_child_of_type<DOM::Element>([&](auto& child) {
             elements.append(&child);
+            return IterationDecision::Continue;
         });
     }
 

Userland/Libraries/LibWeb/HTML/HTMLInputElement.cpp

@@ -135,6 +135,7 @@ void HTMLInputElement::set_checked(bool checked, ChangeSource change_source)
     if (parent()) {
         parent()->for_each_child([&](auto& child) {
             child.invalidate_style();
+            return IterationDecision::Continue;
         });
     }
 }

Userland/Libraries/LibWeb/HTML/HTMLOptionElement.cpp

@@ -85,6 +85,7 @@ static void concatenate_descendants_text_content(DOM::Node const* node, StringBu
         builder.append(verify_cast<DOM::Text>(node)->data());
     node->for_each_child([&](auto const& node) {
         concatenate_descendants_text_content(&node, builder);
+        return IterationDecision::Continue;
     });
 }
 
@@ -98,6 +99,7 @@ String HTMLOptionElement::text() const
     // script or SVG script elements.
     for_each_child([&](auto const& node) {
         concatenate_descendants_text_content(&node, builder);
+        return IterationDecision::Continue;
     });
 
     // Return the result of stripping and collapsing ASCII whitespace from the above concatenation.

Userland/Libraries/LibWeb/HTML/HTMLSelectElement.cpp

@@ -174,12 +174,15 @@ Vector<JS::Handle<HTMLOptionElement>> HTMLSelectElement::list_of_options() const
 
     for_each_child_of_type<HTMLOptionElement>([&](HTMLOptionElement& option_element) {
         list.append(JS::make_handle(option_element));
+        return IterationDecision::Continue;
     });
 
     for_each_child_of_type<HTMLOptGroupElement>([&](HTMLOptGroupElement const& optgroup_element) {
         optgroup_element.for_each_child_of_type<HTMLOptionElement>([&](HTMLOptionElement& option_element) {
             list.append(JS::make_handle(option_element));
+            return IterationDecision::Continue;
         });
+        return IterationDecision::Continue;
     });
 
     return list;

Userland/Libraries/LibWeb/HTML/HTMLTemplateElement.cpp

@@ -58,6 +58,8 @@ void HTMLTemplateElement::cloned(Node& copy, bool clone_children)
 
         // FIXME: Should this use TreeNode::append_child instead?
         MUST(template_clone.content()->append_child(cloned_child));
+
+        return IterationDecision::Continue;
     });
 }
 

Userland/Libraries/LibWeb/HTML/Parser/HTMLParser.cpp

@@ -4418,7 +4418,8 @@ String HTMLParser::serialize_html_fragment(DOM::Node const& node, DOM::FragmentS
         if (is<DOM::Element>(current_node)) {
             // -> If current node is an Element
             auto& element = verify_cast<DOM::Element>(current_node);
-            return serialize_element(element);
+            serialize_element(element);
+            return IterationDecision::Continue;
         }
 
         if (is<DOM::Text>(current_node)) {
@@ -4440,7 +4441,6 @@ String HTMLParser::serialize_html_fragment(DOM::Node const& node, DOM::FragmentS
 
             // 2. Otherwise, append the value of current node's data IDL attribute, escaped as described below.
             builder.append(escape_string(text_node.data(), AttributeMode::No));
-            return IterationDecision::Continue;
         }
 
         if (is<DOM::Comment>(current_node)) {