permissions: evaluate solution for using generators in serializers

[zzacharo]

In the context of serializers, one has access only to the dictionary of data e.g community result item dict. That causes some troubles with permission generators that assume class instance attributes e.g community.access systemfield.

Recently, to implement the permission check in the UICommunitySerializer, see _community_permission_check we changed the IfPolicyClosed generator to search for the fields in

• record.access if the record has an access attribute,
• record.get("access") otherwise

That solution seems not ideal and we should evaluate if this the way to go thus normalize also the other places where the same problem occurs or find a more elegant solution.