LibWeb: Add styleSheets and adoptedStyleSheets attributes in ShadowRoot

Co-authored-by: Simon Wanner <simon+git@skyrising.xyz>

Userland/Libraries/LibWeb/DOM/AdoptedStyleSheets.h

@@ -0,0 +1,16 @@
+/*
+ * Copyright (c) 2024, Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/Forward.h>
+#include <LibWeb/WebIDL/ObservableArray.h>
+
+namespace Web::DOM {
+
+JS::NonnullGCPtr<WebIDL::ObservableArray> create_adopted_style_sheets_list(Document& document);
+
+}