LibWeb/LibJS: Avoid GC visit of raw pointers where possible

This is mostly motivated for aesthetics, but also helps avoid some null
checks when we have a NonnullGCPtr<T> or in some cases a T&.

Userland/Libraries/LibWeb/URL/URL.cpp

@@ -91,7 +91,7 @@ void URL::initialize(JS::Realm& realm)
 void URL::visit_edges(Cell::Visitor& visitor)
 {
     Base::visit_edges(visitor);
-    visitor.visit(m_query.ptr());
+    visitor.visit(m_query);
 }
 
 // https://w3c.github.io/FileAPI/#dfn-createObjectURL