Issue #2747177 by markdorison, chx, Sonal.Sangale, andypost, joachim, Berdir,...
Issue #2747177 by markdorison, chx, Sonal.Sangale, andypost, joachim, Berdir, eojthebrave: Add docs on possible values of $operation in hook_entity_field_access()
(cherry picked from commit 71ca3778)