bad suggestion line for `use` statements with a derive

[arielb1]

#[derive(Debug)]
pub struct X;

impl Add for X {} // trigger unused import

fn main() {}

After #44215, this gives the following error message:

error[E0405]: cannot find trait `Add` in this scope
 --> x.rs:4:6
  |
4 | impl Add for X {} // trigger unused import
  |      ^^^ not found in this scope
  |
help: possible candidate is found in another module, you can import it into scope
  |
2 | use std::ops::Add; // <--- LINE 2 HERE
  |

error: cannot continue compilation due to previous error

This suggests placing the use-statement at line 2, which is between the #[derive] and the pub struct X; line, while we want to place the use statement before the #[derive].

cc @oli-obk

[arielb1]

This remains after the regression in #44566 was fixed.

[oli-obk]

As mentioned in #44566, this is impossible to fix right now, because these attributes do not exist anymore at the lint stage. Solutions are noted in #44215 (comment)

[euclio]

cc #45216.

[programmerjake]

Can this be given a higher priority, it seems to me like a big gotcha for beginners.

An additional way to fix this might be to track the location where use and similar statements should be inserted in blocks, rather than taking the first token of the first post-expansion item. This avoids the need to keep attributes post-expansion.

[compiler-errors]

This now suggests the right span.

error[[E0405]](https://doc.rust-lang.org/stable/error-index.html#E0405): cannot find trait `Add` in this scope
 --> src/main.rs:4:6
  |
4 | impl Add for X {} // trigger unused import
  |      ^^^ not found in this scope
  |
help: consider importing one of these items
  |
1 | [use core::ops::Add;](https://play.rust-lang.org/?version=stable&mode=debug&edition=2018#)
  |
1 | [use nom::lib::std::ops::Add;](https://play.rust-lang.org/?version=stable&mode=debug&edition=2018#)
  |
1 | [use pin_utils::core_reexport::ops::Add;](https://play.rust-lang.org/?version=stable&mode=debug&edition=2018#)
  |
1 | [use std::ops::Add;](https://play.rust-lang.org/?version=stable&mode=debug&edition=2018#)
  |