LibWeb/IDB: Implement IDBCursor::effective_key

Author: https://github.com/stelar7
Commit: 141093e032
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4650
Reviewed-by: https://github.com/AtkinsSJ ✅

Libraries/LibWeb/IndexedDB/IDBCursor.h

@@ -42,6 +42,7 @@ public:
 
     [[nodiscard]] GC::Ref<IDBTransaction> transaction();
     [[nodiscard]] CursorSource internal_source();
+    [[nodiscard]] GC::Ref<Key> effective_key() const;
 
     void set_request(GC::Ptr<IDBRequest> request) { m_request = request; }
     void set_position(GC::Ptr<Key> position) { m_position = position; }