Error on "Add block" link

Working on it.

I was able to reproduce this issue while using Add block button.
So i updated the function such that it is also backward compatible.
Please review.

Perhaps the Deprecation Helper class can be used here? https://www.drupal.org/node/3379306 →

I added the use of the DeprecationHelper. I left in the class_exists and function_exists otherwise the IDE would complain it couldn't find the class (on D10) or the function (on D11).
This module is also only going to support 10.3 (I need to update the info.yml for this in another issue).

For me it's is working fine. and looking backward compatible. so moving it to the RTBC

Merged in dev.