Private items with a public reexport could suggest the public path in privacy error message

E.g. use std::io::buffered::BufferedReader; says struct BufferedReader is private but could say

struct BufferedReader is private, but available publicly as `std::io::BufferedReader`

(This probably requires some significant work, for not a huge benefit.)

1. Triage: no change here, these kinds of messages still happen.

   Steve Klabnik at 2015-04-28 18:13:11

2. Triage: no change

   Steve Klabnik at 2017-01-03 17:26:26

3. Triage: no change

   Steve Klabnik at 2018-09-24 15:46:34

4. Triage: no change

   Ryan Levick at 2021-07-05 09:43:47

5. Current output: no real change with 1.65.0-nightly (2022-08-10 29e4a9ee0253cd39e552):

   use std::io::buffered::BufReader;
   

   error[[E0603]](https://doc.rust-lang.org/nightly/error-index.html#E0603): module `buffered` is private
    --> src/lib.rs:1:14
     |
   1 | [use std::io::buffered::BufReader;](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021#)
     |              ^^^^^^^^ private module
     |
   note: the module `buffered` is defined here
   

   TimJentzsch at 2022-08-11 13:47:41