AK: Add contains_slow method to Stack

Author: https://github.com/cflip
Commit: https://github.com/SerenityOS/serenity/commit/9a0bb8212a
Pull-request: https://github.com/SerenityOS/serenity/pull/16061
Reviewed-by: https://github.com/gmta ✅

AK/Stack.h

@@ -63,6 +63,11 @@ public:
         return m_stack.last();
     }
 
+    bool contains_slow(T const& value) const
+    {
+        return m_stack.contains_slow(value);
+    }
+
 private:
     Vector<T, stack_size> m_stack;
 };