Consider detecting when content types could use a resave and notify users.

[tw2113]

Source: https://wordpress.org/support/topic/replacing-plugin-with-cptui_register_my_cpts-doesnt-work/#post-12424251

Basically the user had some older post types that didn't have all the indexes for the version at the time. Because of that, get code functionality was missing some values that were expected.

This could also help with future cases of undefined index warnings.

So, if we have a release that introduces new fields, either notify everyone right away, or do a scan of existing option values to notify.

[tw2113]

Closing the previous PR attempt, as I believe that was going in a direction that we didn't need to, in the end.

Leaving as a future release as I don't have strong feelings on this, but there is at least some potential need, depending on how we settle on handling.