#2317193 | Port "Add an item to a list" action to D8

Initial port
> The UserHasEntityFieldAccessTest.php should be fixed in 8.x-3.x, please merge your branch.

Ah - I think the issue here is I fetched the upstream and rebased to my local 8.x-3.x but of course this is a branch so I'll need to now rebase that branch on the latest 8.x-3.x.

> The outputlist provided context is missing here? Same for the other contexts in the annotation?

The 'pos' and 'unique' contexts aren't required - I take it then I still have to declare them here. Thanks for the pointer.