Drupal 11 compatibility

As I searched through, I did not find a D11 upgrade ticket in the module's issue queue, so thought it was better to collect all the necessary compatibility changes under one roof.

Pipeline green on the merge request, marking as Needs Review.

samit.310@gmail.com → made their first commit to this issue’s fork.

Now tested on a D11-beta1 site locally with 2 different user accounts, the one with some lower level of permissions has no access to modify the protected field on the form at all. However, leaving the ticket on NR as I am not allowed to mark for RTBC due to my previous involvement.

Tests need to be rewritten as dataProviders must be static, making the design for test doubles not workable.
https://stackoverflow.com/questions/76853088/how-to-create-test-doubles-...

Reverted my commit d18d84bd as it was a misunderstanding we just now cleared out with @japerry → .

Automatically closed - issue fixed for 2 weeks with no activity.