AK+Everywhere: Remove the null state of DeprecatedString

This commit removes DeprecatedString's "null" state, and replaces all
its users with one of the following:
- A normal, empty DeprecatedString
- Optional<DeprecatedString>

Note that null states of DeprecatedFlyString/StringView/etc are *not*
affected by this commit. However, DeprecatedString::empty() is now
considered equal to a null StringView.

Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp

@@ -1092,10 +1092,11 @@ void BlockFormattingContext::layout_list_item_marker(ListItemBox const& list_ite
 
     CSSPixels default_marker_width = max(4, marker.font().pixel_size_rounded_up() - 4);
 
-    if (marker.text().is_empty()) {
+    auto marker_text = marker.text().value_or("");
+    if (marker_text.is_empty()) {
         marker_state.set_content_width(image_width + default_marker_width);
     } else {
-        auto text_width = marker.font().width(marker.text());
+        auto text_width = marker.font().width(marker_text);
         marker_state.set_content_width(image_width + CSSPixels::nearest_value_for(text_width));
     }
 

Userland/Libraries/LibWeb/Layout/Label.cpp

@@ -93,7 +93,7 @@ Label const* Label::label_for_control_node(LabelableNode const& control)
     // same tree as the label element. If the attribute is specified and there is an element in the tree
     // whose ID is equal to the value of the for attribute, and the first such element in tree order is
     // a labelable element, then that element is the label element's labeled control.
-    if (auto id = control.dom_node().deprecated_attribute(HTML::AttributeNames::id); !id.is_empty()) {
+    if (auto id = control.dom_node().attribute(HTML::AttributeNames::id); id.has_value() && !id->is_empty()) {
         Label const* label = nullptr;
 
         control.document().layout_node()->for_each_in_inclusive_subtree_of_type<Label>([&](auto& node) {
@@ -126,9 +126,9 @@ LabelableNode* Label::labeled_control()
     // same tree as the label element. If the attribute is specified and there is an element in the tree
     // whose ID is equal to the value of the for attribute, and the first such element in tree order is
     // a labelable element, then that element is the label element's labeled control.
-    if (auto for_ = dom_node().for_(); !for_.is_null()) {
+    if (auto for_ = dom_node().for_(); for_.has_value()) {
         document().layout_node()->for_each_in_inclusive_subtree_of_type<LabelableNode>([&](auto& node) {
-            if (node.dom_node().deprecated_attribute(HTML::AttributeNames::id) == for_) {
+            if (node.dom_node().attribute(HTML::AttributeNames::id) == for_) {
                 control = &node;
                 return IterationDecision::Break;
             }

Userland/Libraries/LibWeb/Layout/ListItemMarkerBox.h

@@ -18,7 +18,7 @@ public:
     explicit ListItemMarkerBox(DOM::Document&, CSS::ListStyleType, CSS::ListStylePosition, size_t index, NonnullRefPtr<CSS::StyleProperties>);
     virtual ~ListItemMarkerBox() override;
 
-    DeprecatedString const& text() const { return m_text; }
+    Optional<DeprecatedString> const& text() const { return m_text; }
 
     virtual JS::GCPtr<Painting::Paintable> create_paintable() const override;
 
@@ -33,7 +33,7 @@ private:
     CSS::ListStylePosition m_list_style_position { CSS::ListStylePosition::Outside };
     size_t m_index;
 
-    DeprecatedString m_text {};
+    Optional<DeprecatedString> m_text {};
 };
 
 template<>

Userland/Libraries/LibWeb/Layout/TextNode.cpp

@@ -306,9 +306,9 @@ void TextNode::invalidate_text_for_rendering()
 
 DeprecatedString const& TextNode::text_for_rendering() const
 {
-    if (m_text_for_rendering.is_null())
+    if (!m_text_for_rendering.has_value())
         const_cast<TextNode*>(this)->compute_text_for_rendering();
-    return m_text_for_rendering;
+    return *m_text_for_rendering;
 }
 
 // NOTE: This collapses whitespace into a single ASCII space if the CSS white-space property tells us to.

Userland/Libraries/LibWeb/Layout/TextNode.h

@@ -55,7 +55,7 @@ public:
 private:
     virtual bool is_text_node() const final { return true; }
 
-    DeprecatedString m_text_for_rendering;
+    Optional<DeprecatedString> m_text_for_rendering;
 };
 
 template<>