LibWeb: Implement a CSS::Number class

We have the same "number and is-integer flag" structure in several
places, so let's put that in a class.

Userland/Libraries/LibWeb/CSS/Number.h

@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+#include <math.h>
+
+namespace Web::CSS {
+
+class Tokenizer;
+
+class Number {
+    friend class Tokenizer;
+
+public:
+    enum class Type {
+        Number,
+        IntegerWithExplicitSign, // This only exists for the nightmarish An+B parsing algorithm
+        Integer
+    };
+
+    Number()
+        : m_value(0)
+        , m_type(Type::Number)
+    {
+    }
+    Number(Type type, float value)
+        : m_value(value)
+        , m_type(type)
+    {
+    }
+
+    float value() const { return m_value; }
+    i64 integer_value() const
+    {
+        // https://www.w3.org/TR/css-values-4/#numeric-types
+        // When a value cannot be explicitly supported due to range/precision limitations, it must be converted
+        // to the closest value supported by the implementation, but how the implementation defines "closest"
+        // is explicitly undefined as well.
+        return llroundf(m_value);
+    }
+    bool is_integer() const { return m_type == Type::Integer || m_type == Type::IntegerWithExplicitSign; }
+    bool is_integer_with_explicit_sign() const { return m_type == Type::IntegerWithExplicitSign; }
+
+    Number operator+(Number const& other) const
+    {
+        if (is_integer() && other.is_integer())
+            return { Type::Integer, m_value + other.m_value };
+        return { Type::Number, m_value + other.m_value };
+    }
+
+    Number operator-(Number const& other) const
+    {
+        if (is_integer() && other.is_integer())
+            return { Type::Integer, m_value - other.m_value };
+        return { Type::Number, m_value - other.m_value };
+    }
+
+    Number operator*(Number const& other) const
+    {
+        if (is_integer() && other.is_integer())
+            return { Type::Integer, m_value * other.m_value };
+        return { Type::Number, m_value * other.m_value };
+    }
+
+    Number operator/(Number const& other) const
+    {
+        return { Type::Number, m_value / other.m_value };
+    }
+
+    auto operator<=>(Number const& other) const
+    {
+        return m_value - other.m_value;
+    }
+
+private:
+    float m_value { 0 };
+    Type m_type;
+};
+}

Userland/Libraries/LibWeb/Forward.h

@@ -59,6 +59,7 @@ class MediaList;
 class MediaQuery;
 class MediaQueryList;
 class MediaQueryListEvent;
+class Number;
 class NumericStyleValue;
 class OverflowStyleValue;
 class Percentage;