Rollup merge of #146123 - IoaNNUwU:issue-68293, r=estebank

Suggest examples of format specifiers in error messages

Format macro now suggests adding `{}` if no formatting specifiers are present. It also gives an example:
```rust
LL |     println!("Hello", "World");
   |              -------  ^^^^^^^ argument never used
   |              |
   |              formatting specifier missing
   |
   = note: format specifiers use curly braces: `{}`
help: consider adding format specifier
   |
LL |     println!("Hello{}", "World");
   |                    ++
```
When one or more `{}` are present, it doesn't show 'format specifiers use curly braces: `{}`' and example, just small hint on how many you missing:
```rust
LL |     println!("list: {}", 1, 2, 3);
   |              ----------     ^  ^ argument never used
   |              |              |
   |              |              argument never used
   |              multiple missing formatting specifiers
   |
   = help: consider adding 2 format specifiers
```

Original issue: rust-lang/rust#68293
Based on discussion in this PR: rust-lang/rust#76443

Let me know if something is missing

Author: matthiaskrgr