LibWeb: Implement adoptedStyleSheets attribute for Document

https://drafts.csswg.org/cssom/#dom-documentorshadowroot-adoptedstylesheets

The attribute implementation for ShadowRoot is currently missing
because we do not yet distinguish between the style sheets of
ShadowRoot and Document, and we need to address the issue first.

Userland/Libraries/LibWeb/CSS/StyleComputer.cpp

@@ -266,8 +266,9 @@ void StyleComputer::for_each_stylesheet(CascadeOrigin cascade_origin, Callback c
             callback(*m_user_style_sheet);
     }
     if (cascade_origin == CascadeOrigin::Author) {
-        for (auto const& sheet : document().style_sheets().sheets())
-            callback(*sheet);
+        document().for_each_css_style_sheet([&](CSSStyleSheet& sheet) {
+            callback(sheet);
+        });
     }
 }