Allow saving pre-existing references to inaccessible items

rp7 → changed the visibility of the branch 2909747-allow-saving-pre-existing to hidden.

rp7 → changed the visibility of the branch 2909747-allow-saving-pre-existing to active.

rp7 → changed the visibility of the branch 2909747-allow-saving-pre-existing to hidden.

I opened a merge request. This is basically a copy of how core does it concerning previously referenced items.

This MR also contains the changes needed for 🐛 ValidDynamicReferenceConstraintValidator doesn't pass correct entity to selection handler Active , as we need it in order to be able to load the correct unchanged entity.

PS: I'd like to suggest opening up another issue to make use of

EntityStorageInterface::loadMultiple()

in the whole of ValidDynamicReferenceConstraintValidator. I'm convinced this can greatly enhance validation performance for dynamic entity reference fields containing a lot of references (to the same target type).