Lint for Iterator + Copy

[sinkuu]

Implementing Copy for iterators makes footguns, and the standard library settled not to do so for now.

let mut it = /* a Copy + Iterator */;
for x in it { if cond { break; } } // `it` copied here (forgot to `&mut it`)
let x = it.next(); // `it` is in the initial state

Clippy should have a lint that warns if "use of the original iterator after copied" is detected.

[oli-obk]

The E-easy part of this is a lint triggering on any type that implements Iterator and Copy at the same time. The E-medium part is a lint triggering only on the duplicate use.