LibWeb: Use HTML-uppercased qualified name for the Element node name

For regular elements, this is just the qualified name.
However, for HTML elements in HTML documents, it is the qualified name
uppercased.

This is used by jQuery to determine the document is an HTML document.
Not having this made jQuery assume the document was XML, causing
weird behaviour.

To do this, an internal string of qualified name is created.
This is to prevent constantly regenerating it. This is allowed by
the spec.

This is the same for the HTML-uppercased qualified name.

Userland/Libraries/LibWeb/DOM/Element.cpp

@@ -34,6 +34,7 @@ Element::Element(Document& document, QualifiedName qualified_name)
     : ParentNode(document, NodeType::ELEMENT_NODE)
     , m_qualified_name(move(qualified_name))
 {
+    make_html_uppercased_qualified_name();
 }
 
 Element::~Element()
@@ -359,4 +360,14 @@ NonnullRefPtr<CSS::CSSStyleDeclaration> Element::style_for_bindings()
     return *m_inline_style;
 }
 
+// https://dom.spec.whatwg.org/#element-html-uppercased-qualified-name
+void Element::make_html_uppercased_qualified_name()
+{
+    // This is allowed by the spec: "User agents could optimize qualified name and HTML-uppercased qualified name by storing them in internal slots."
+    if (namespace_() == Namespace::HTML /* FIXME: and its node document is an HTML document */)
+        m_html_uppercased_qualified_name = qualified_name().to_uppercase();
+    else
+        m_html_uppercased_qualified_name = qualified_name();
+}
+
 }

Userland/Libraries/LibWeb/DOM/Element.h

@@ -29,7 +29,9 @@ public:
     Element(Document&, QualifiedName);
     virtual ~Element() override;
 
-    virtual FlyString node_name() const final { return m_qualified_name.local_name(); }
+    const String& qualified_name() const { return m_qualified_name.as_string(); }
+    String html_uppercased_qualified_name() const { return m_html_uppercased_qualified_name; }
+    virtual FlyString node_name() const final { return html_uppercased_qualified_name(); }
     const FlyString& local_name() const { return m_qualified_name.local_name(); }
 
     // NOTE: This is for the JS bindings
@@ -96,7 +98,10 @@ private:
     Attribute* find_attribute(const FlyString& name);
     const Attribute* find_attribute(const FlyString& name) const;
 
+    void make_html_uppercased_qualified_name();
+
     QualifiedName m_qualified_name;
+    String m_html_uppercased_qualified_name;
     Vector<Attribute> m_attributes;
 
     RefPtr<CSS::CSSStyleDeclaration> m_inline_style;

Userland/Libraries/LibWeb/QualifiedName.h

@@ -17,16 +17,33 @@ public:
         , m_prefix(prefix)
         , m_namespace(namespace_)
     {
+        make_internal_string();
     }
 
     const FlyString& local_name() const { return m_local_name; }
     const FlyString& prefix() const { return m_prefix; }
     const FlyString& namespace_() const { return m_namespace; }
 
+    const String& as_string() const { return m_as_string; }
+
 private:
     FlyString m_local_name;
     FlyString m_prefix;
     FlyString m_namespace;
+    String m_as_string;
+
+    // https://dom.spec.whatwg.org/#concept-attribute-qualified-name
+    // https://dom.spec.whatwg.org/#concept-element-qualified-name
+    void make_internal_string()
+    {
+        // This is possible to do according to the spec: "User agents could have this as an internal slot as an optimization."
+        if (m_prefix.is_null()) {
+            m_as_string = m_local_name;
+            return;
+        }
+
+        m_as_string = String::formatted("{}:{}", m_prefix, m_local_name);
+    }
 };
 
 }