LibWeb: Add method to absolutize CalculatedOr

Author: https://github.com/Calme1709
Commit: c8bd58c0ba
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5699
Reviewed-by: https://github.com/AtkinsSJ ✅

Libraries/LibWeb/CSS/CalculatedOr.h

@@ -78,6 +78,20 @@ public:
             });
     }
 
+    Self absolutized(CSSPixelRect const& viewport_rect, Length::FontMetrics const& font_metrics, Length::FontMetrics const& root_font_metrics) const
+    {
+        return m_value.visit(
+            [&](T const& value) {
+                if constexpr (IsSame<T, Length>)
+                    return Self { value.absolutized(viewport_rect, font_metrics, root_font_metrics) };
+                else
+                    return *static_cast<Self const*>(this);
+            },
+            [&](NonnullRefPtr<CalculatedStyleValue const> const& value) {
+                return Self { value->absolutized(viewport_rect, font_metrics, root_font_metrics)->as_calculated() };
+            });
+    }
+
     bool operator==(CalculatedOr<Self, T> const& other) const
     {
         if (is_calculated() || other.is_calculated())