Introduce a deprecation framework for driconf options
When a driconf option becomes superseeded by another one, it is beneficial to drop it from the codebase to remove useless code. However, users with the now-removed options in their local .drirc will be left wondering why an OS update broke their game/app. To mitigate this, this patch series adds a warning to tell users that the option is deprecated and what to do to fix their drirc!
This series is meant to land after !7212 (merged) and is separate as I think this is the first time an option is deprecated and I expect there will be a certain amount of discussion around it :)