LibWeb: Use rect value in CSS clip property

When a rect value is passed to the clip property via CSS, keep it in
ComputedValues so that at a later stage can make use of it.

Userland/Libraries/LibWeb/CSS/Clip.h

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2022, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/CSS/StyleValue.h>
+
+namespace Web::CSS {
+
+class Clip {
+public:
+    enum class Type {
+        Auto,
+        Rect
+    };
+
+    Clip(Type type, EdgeRect edge_rect);
+    Clip(EdgeRect edge_rect);
+
+    static Clip make_auto();
+
+    bool is_auto() const { return m_type == Type::Auto; }
+    bool is_rect() const { return m_type == Type::Rect; }
+
+    EdgeRect to_rect() const { return m_edge_rect; }
+
+private:
+    Type m_type;
+    EdgeRect m_edge_rect;
+};
+
+}