Unified Mode on by default for Custom Resources (in Chef-18)
This needs to be done in phases.
For Chef 17 we need to get more aggressive about cookbooks needing to declare unifed_mode one way or the other. Since we have so much Chef-12 concerns and sous-chefs have still never EOL'd Chef 12, that means we need to support Chef 12, that means we must have a cop that enforces at least:
unified_mode false if respond_to?(:unified_mode)
Which is terrible, but without hard dropping Chef-12 support we can't do anything else.
We should also warn on users not setting unified_mode on resources one way or the other in Chef 15 + Chef 16 + Chef 17 (XXX: maybe not Chef-15 since not all the internal resources are unified_mode there)
@chef/chef-infra-approvers this can be closed now. Sous have basically dropped support for anything pre-15.3