Overly verbose suggestion display for trailing whitespace changes

When a suggestion removes a line the diff suggests removing and re-adding the previous line. We do these kinds of suggestions a fair bit in clippy to make --fix actually remove the line.

e.g. in needless_return the code:

fn main() {
    if true {
        println!("foo");
        return;
    } else {
        println!("bar");
    }
}

Gives the suggestion:

 --> src/main.rs:3:25
  |
3 |           println!("foo");
  |  _________________________^
4 | |         return;
  | |______________^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_return
  = note: `#[warn(clippy::needless_return)]` on by default
help: remove `return`
  |
3 -         println!("foo");
4 -         return;
3 +         println!("foo");
  |

This suggests to remove and re-add println!("foo"); rather than just remove the return line. The lint span spanning multiple lines is entirely on clippy, but the suggestion display can't be fixed by us.

cc rust-lang/rust-clippy#14750

Reproduce the needless_return example and inspect the compiler's suggestion-display path, using the linked rust-clippy#14750 context to understand the multi-line span. Done means the displayed suggestion removes only return instead of removing and re-adding the unchanged println!("foo"); line.