Prevent the changed date of entities to be updating when removing a reference

Really nice feature to have, thanks!

Pushed a commit to add a missing import.

Can you add a test for this? It seems pretty straightforward.

Actually I cannot reproduce the problem on Drupal 11.2.

Calling $entity->save() doesn't seem to update the changed timestamp.

@dieterholvoet could you provide a detailed scenario to reproduce the problem on a fresh Drupal 11 instance?

EDIT: Ok, it looks like it's because I'm creating and updating the node in the same request, so the \Drupal::time()->getRequestTime() value is the same when updating the node...

Tried to implement some basic changed timestamp preservation tests.

Added a basic test time service to allow changing the request time during test.

I'm not a test expert, so any feedback will be greatly appreciated.