Auto merge of #40851 - oli-obk:multisugg, r=jonathandturner

Auto merge of #40851 - oli-obk:multisugg, r=jonathandturner

Minimize single span suggestions into a label

changes

```
14 |     println!("☃{}", tup[0]);
   |                     ^^^^^^
   |
help: to access tuple elements, use tuple indexing syntax as shown
   |     println!("☃{}", tup.0);
```

into

```
14 |     println!("☃{}", tup[0]);
   |                     ^^^^^^ to access tuple elements, use `tup.0`
```

Also makes suggestions explicit in the backend in preparation of adding multiple suggestions to a single diagnostic. Currently that's already possible, but results in a full help message + modified code snippet per suggestion, and has no rate limit (might show 100+ suggestions).