Backports the interface and trait from #31805 (N.B. Don't merge this until that other PR is merged)
Note I've not backported the methods in the interface as it doesn't matter (as it's just a placeholder) and with the current approach it gives PHP 5.4 compatibility but with the interfaces included in Joomla 4 it would require PHP 7.0 which is an unnecessary requirement
Documentation Changes Required
Yup but should be covered as part of the linked J4 ticket
Merging the empty classes into 3.10 now given that the upstream PR into 4.x have been merged in the meantime.