LibWeb: Don't include Layout/Node.h from DOM/Element.h

This required moving the CSS::StyleProperty destruct out of line.

Userland/Libraries/LibWeb/CSS/StyleProperty.cpp

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) 2023, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/CSS/StyleProperty.h>
+#include <LibWeb/CSS/StyleValue.h>
+
+namespace Web::CSS {
+
+StyleProperty::~StyleProperty() = default;
+
+}