Rollup merge of #140598 - ShE3py:iter-misc-docs, r=workingjubilee

Steer docs to `utf8_chunks` and `Iterator::take`

- Adds `limit` as an alias of `take` (as this is [what Java calls this operation](https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#limit-long-));
- Says that [`Utf8Chunks`](https://doc.rust-lang.org/std/str/struct.Utf8Chunks.html) comes from [`[u8]::utf8_chunks`](https://doc.rust-lang.org/std/primitive.slice.html#method.utf8_chunks).

``@rustbot`` label +A-docs

Author: Zalathar