LibJS: Add Visitor::visit(GCPtr<T>) and Visitor::visit(NonnullGCPtr<T>)

Let's avoid reaching for ptr() as much as possible.

Userland/Libraries/LibJS/Heap/Cell.h

@@ -11,6 +11,7 @@
 #include <AK/Noncopyable.h>
 #include <AK/StringView.h>
 #include <LibJS/Forward.h>
+#include <LibJS/Heap/GCPtr.h>
 
 namespace JS {
 
@@ -55,6 +56,17 @@ public:
         {
             visit_impl(cell);
         }
+        template<typename T>
+        void visit(GCPtr<T> cell)
+        {
+            if (cell)
+                visit_impl(*cell.ptr());
+        }
+        template<typename T>
+        void visit(NonnullGCPtr<T> cell)
+        {
+            visit_impl(*cell.ptr());
+        }
         void visit(Value);
 
     protected:

Userland/Libraries/LibJS/Runtime/FinalizationRegistry.cpp

@@ -82,7 +82,7 @@ ThrowCompletionOr<void> FinalizationRegistry::cleanup(Optional<JobCallback> call
 void FinalizationRegistry::visit_edges(Cell::Visitor& visitor)
 {
     Base::visit_edges(visitor);
-    visitor.visit(m_realm.ptr());
+    visitor.visit(m_realm);
     for (auto& record : m_records) {
         visitor.visit(record.held_value);
         visitor.visit(record.unregister_token);