Deletion of used QuantityValue warning is missing

https://github.com/pimcore/pimcore/pull/16836 should add a warning if a used QuantityValue gets deleted.
I tested it with a quantity value that was used inside a classification store and there was no warning.

<img width="1226" height="896" alt="Image" src="https://github.com/user-attachments/assets/70caf883-208e-46c7-8498-b9bfbc3525d9" />

Tested on nightly26