LibWeb: Use Element::namespace_ instead of ELement::namespace_uri

These are equivalent, and should make our lives a little eaiser porting
over this IDL interface to new String.

Userland/Libraries/LibWeb/CSS/StyleComputer.cpp

@@ -277,7 +277,7 @@ StyleComputer::RuleCache const& StyleComputer::rule_cache_for_cascade_origin(Cas
 {
     // FIXME: Filter out non-default namespace using prefixes
     auto namespace_uri = rule.sheet->default_namespace();
-    if (namespace_uri.has_value() && namespace_uri.value() != element.namespace_uri()) {
+    if (namespace_uri.has_value() && namespace_uri.value() != element.namespace_()) {
         return false;
     }
     return true;

Userland/Libraries/LibWeb/DOM/Element.cpp

@@ -175,7 +175,7 @@ WebIDL::ExceptionOr<void> Element::set_attribute(DeprecatedFlyString const& name
 
     // 2. If this is in the HTML namespace and its node document is an HTML document, then set qualifiedName to qualifiedName in ASCII lowercase.
     // FIXME: Handle the second condition, assume it is an HTML document for now.
-    bool insert_as_lowercase = namespace_uri() == Namespace::HTML;
+    bool insert_as_lowercase = namespace_() == Namespace::HTML;
 
     // 3. Let attribute be the first attribute in this’s attribute list whose qualified name is qualifiedName, and null otherwise.
     auto* attribute = m_attributes->get_attribute(name);
@@ -328,7 +328,7 @@ WebIDL::ExceptionOr<bool> Element::toggle_attribute(DeprecatedFlyString const& n
 
     // 2. If this is in the HTML namespace and its node document is an HTML document, then set qualifiedName to qualifiedName in ASCII lowercase.
     // FIXME: Handle the second condition, assume it is an HTML document for now.
-    bool insert_as_lowercase = namespace_uri() == Namespace::HTML;
+    bool insert_as_lowercase = namespace_() == Namespace::HTML;
 
     // 3. Let attribute be the first attribute in this’s attribute list whose qualified name is qualifiedName, and null otherwise.
     auto* attribute = m_attributes->get_attribute(name);

Userland/Libraries/LibWeb/DOM/NamedNodeMap.cpp

@@ -60,7 +60,7 @@ Vector<DeprecatedString> NamedNodeMap::supported_property_names() const
 
     // 2. If this NamedNodeMap object’s element is in the HTML namespace and its node document is an HTML document, then for each name in names:
     // FIXME: Handle the second condition, assume it is an HTML document for now.
-    if (associated_element().namespace_uri() == Namespace::HTML) {
+    if (associated_element().namespace_() == Namespace::HTML) {
         // 1. Let lowercaseName be name, in ASCII lowercase.
         // 2. If lowercaseName is not equal to name, remove name from names.
         names.remove_all_matching([](auto const& name) { return name != name.to_lowercase(); });
@@ -157,7 +157,7 @@ Attr const* NamedNodeMap::get_attribute(StringView qualified_name, size_t* item_
 
     // 1. If element is in the HTML namespace and its node document is an HTML document, then set qualifiedName to qualifiedName in ASCII lowercase.
     // FIXME: Handle the second condition, assume it is an HTML document for now.
-    bool compare_as_lowercase = associated_element().namespace_uri() == Namespace::HTML;
+    bool compare_as_lowercase = associated_element().namespace_() == Namespace::HTML;
 
     // 2. Return the first attribute in element’s attribute list whose qualified name is qualifiedName; otherwise null.
     for (auto const& attribute : m_attributes) {

Userland/Libraries/LibWeb/DOMParsing/XMLSerializer.cpp

@@ -526,7 +526,7 @@ static WebIDL::ExceptionOr<DeprecatedString> serialize_element(DOM::Element cons
     auto inherited_ns = namespace_;
 
     // 10. Let ns be the value of node's namespaceURI attribute.
-    auto const& ns = element.namespace_uri();
+    auto const& ns = element.namespace_();
 
     // 11. If inherited ns is equal to ns, then:
     if (inherited_ns == ns) {