auto merge of #19060 : Gankro/rust/super-cloned, r=aturon

Edit: whoops, didn't mean to hit post.

Anyway, this is something I tried to do when I first implemented cloned, but couldn't figure out. Somewhere between then and the PR actually landing, we got Deref of references, so now this works! :tada:

Also turns out the test for the functionality was never marked as a #[test]. Oops!

Also added a Cloned iterator adaptor. If this isn't desirable, it can be taken out of the PR (seperate commits).