Improve display validation errors for fields hidden in tabs

[MegaKeegMan]

This has been an issue both for new content and migrated content. Some content migrated without values in field_created_date and field_authors, which are required fields, so someone might try to edit and save that content, but may not notice that the save button does not do anything if these fields remain empty. There is no validation error that is displayed for the user, and this is particularly problematic in the case where someone does not realize that the save is not occurring when they click save, or how to actually resolve the validation error, potentially putting their changes at risk of being lost.