Meta/CodeGenerators+LibWeb: Implement parsing CSS easing functions

This only implements the parser bits, no functionality is implemented,
and no properties are parsed because of this.

Userland/Libraries/LibWeb/CSS/StyleValues/EasingStyleValue.cpp

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2021, Tobias Christiansen <tobyase@serenityos.org>
+ * Copyright (c) 2021-2023, Sam Atkins <atkinssj@serenityos.org>
+ * Copyright (c) 2022-2023, MacDue <macdue@dueutil.tech>
+ * Copyright (c) 2023, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "EasingStyleValue.h"
+#include <AK/StringBuilder.h>
+
+namespace Web::CSS {
+
+ErrorOr<String> EasingStyleValue::to_string() const
+{
+    if (m_properties.easing_function == EasingFunction::StepStart)
+        return "steps(1, start)"_string;
+    if (m_properties.easing_function == EasingFunction::StepEnd)
+        return "steps(1, end)"_string;
+
+    StringBuilder builder;
+    TRY(builder.try_append(CSS::to_string(m_properties.easing_function)));
+
+    if (m_properties.values.is_empty())
+        return builder.to_string();
+
+    TRY(builder.try_append('('));
+    for (size_t i = 0; i < m_properties.values.size(); ++i) {
+        TRY(builder.try_append(TRY(m_properties.values[i]->to_string())));
+        if (i != m_properties.values.size() - 1)
+            TRY(builder.try_append(", "sv));
+    }
+    TRY(builder.try_append(')'));
+
+    return builder.to_string();
+}
+
+bool EasingStyleValue::Properties::operator==(Properties const& other) const
+{
+    return easing_function == other.easing_function && values == other.values;
+}
+
+}