LibWeb: Use RefPtrs more in getElementById() and getElementsByName()

Passing around Vector<Element*> is not a great idea long-term.

Libraries/LibWeb/DOM/Document.cpp

@@ -359,12 +359,12 @@ void Document::set_hovered_node(Node* node)
     invalidate_style();
 }
 
-Vector<const Element*> Document::get_elements_by_name(const String& name) const
+NonnullRefPtrVector<Element> Document::get_elements_by_name(const String& name) const
 {
-    Vector<const Element*> elements;
+    NonnullRefPtrVector<Element> elements;
     for_each_in_subtree_of_type<Element>([&](auto& element) {
         if (element.attribute(HTML::AttributeNames::name) == name)
-            elements.append(&element);
+            elements.append(element);
         return IterationDecision::Continue;
     });
     return elements;

Libraries/LibWeb/DOM/Document.h

@@ -127,7 +127,7 @@ public:
 
     void schedule_style_update();
 
-    Vector<const Element*> get_elements_by_name(const String&) const;
+    NonnullRefPtrVector<Element> get_elements_by_name(const String&) const;
     NonnullRefPtrVector<Element> get_elements_by_tag_name(const FlyString&) const;
 
     const String& source() const { return m_source; }

Libraries/LibWeb/DOM/NonElementParentNode.h

@@ -36,9 +36,9 @@ namespace Web::DOM {
 template<typename NodeType>
 class NonElementParentNode {
 public:
-    const Element* get_element_by_id(const FlyString& id) const
+    RefPtr<Element> get_element_by_id(const FlyString& id) const
     {
-        const Element* found_element = nullptr;
+        RefPtr<Element> found_element;
         static_cast<const NodeType*>(this)->template for_each_in_subtree_of_type<Element>([&](auto& element) {
             if (element.attribute(HTML::AttributeNames::id) == id) {
                 found_element = &element;
@@ -48,9 +48,9 @@ public:
         });
         return found_element;
     }
-    Element* get_element_by_id(const FlyString& id)
+    RefPtr<Element> get_element_by_id(const FlyString& id)
     {
-        return const_cast<Element*>(const_cast<const NonElementParentNode*>(this)->get_element_by_id(id));
+        return const_cast<const NonElementParentNode*>(this)->get_element_by_id(id);
     }
 
 protected:

Libraries/LibWeb/Page/Frame.cpp

@@ -141,11 +141,11 @@ void Frame::scroll_to_anchor(const String& fragment)
     if (!document())
         return;
 
-    const auto* element = document()->get_element_by_id(fragment);
+    auto element = document()->get_element_by_id(fragment);
     if (!element) {
         auto candidates = document()->get_elements_by_name(fragment);
-        for (auto* candidate : candidates) {
-            if (is<HTML::HTMLAnchorElement>(*candidate)) {
+        for (auto& candidate : candidates) {
+            if (is<HTML::HTMLAnchorElement>(candidate)) {
                 element = downcast<HTML::HTMLAnchorElement>(candidate);
                 break;
             }