Rollup merge of #40092 - sinkuu:fix_suggestion_index, r=pnkfelix

Fix suggestion span error with a line containing multibyte characters

This PR fixes broken suggestions caused by multibyte characters.

e.g. for this code, rustc provides a broken suggestion ([playground](https://is.gd/DWGLu7)):

```rust
fn main() {
    let tup = (1,);
    println!("☃{}", tup[0]);
}
```

```
error: cannot index a value of type `({integer},)`
 --> <anon>:3:21
  |
3 |     println!("☃{}", tup[0]);
  |                     ^^^^^^
  |
help: to access tuple elements, use tuple indexing syntax as shown
  |     println!("☃{}"tup.00]);

error: aborting due to previous error
```

`CodeSuggestion::splice_lines` is misusing `Loc.col` (`CharPos`) as a byte offset when slicing source.

0 files changed, 0 insertions, 0 deletions