Rollup merge of #139780 - ongardie:iterator-take-by_ref-example, r=workingjubilee

docs: Add example to `Iterator::take` with `by_ref`

If you want to logically split an iterator after `n` items, you might first discover `take`. Before this change, you'd find that `take` consumes the iterator, and you'd probably be stuck. The answer involves `by_ref`, but that's hard to discover, especially since `by_ref` is a bit abstract and `Iterator` has many methods.

After this change, you'd see the example showing `take` along with `by_ref`, which allows you to continue using the rest of the iterator. `by_ref` had a good example involving `take` already, so this change just duplicates that existing example under `take`.

Author: GuillaumeGomez