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).
