LibJS+LibWeb: Wrap raw JS::Cell*/& fields in GCPtr/NonnullGCPtr

Author: https://github.com/mattco98
Commit: 7c0c1c8f49
Pull-request: https://github.com/SerenityOS/serenity/pull/17743
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibWeb/CSS/CSSStyleRule.h

@@ -40,7 +40,7 @@ private:
     virtual DeprecatedString serialized() const override;
 
     Vector<NonnullRefPtr<Selector>> m_selectors;
-    CSSStyleDeclaration& m_declaration;
+    JS::NonnullGCPtr<CSSStyleDeclaration> m_declaration;
 };
 
 template<>