LibWeb: Introduce and parse CSS Ratio type

This is only used by media-queries, so for now we can skip
adding/parsing a StyleValue for these.

Userland/Libraries/LibWeb/CSS/Ratio.h

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/String.h>
+
+namespace Web::CSS {
+
+// https://www.w3.org/TR/css-values-4/#ratios
+class Ratio {
+public:
+    Ratio(float first, float second = 1);
+    float value() const { return m_first_value / m_second_value; }
+    bool is_degenerate() const;
+
+    String to_string() const;
+    auto operator<=>(Ratio const& other) const;
+
+private:
+    float m_first_value { 0 };
+    float m_second_value { 1 };
+};
+
+}