Suggest introducing a labeled block when `break` is used outside of a loop, but inside a block

[nagisa]

The following code:

fn main() {
    {
        break ();
    }
}

will output a diagnostic like this:

error[E0268]: `break` outside of a loop
 --> src/main.rs:3:9
  |
3 |         break;
  |         ^^^^^ cannot `break` outside of a loop

No loops in scope here, but there is a possible change that could be made besides adding a loop – introducing labels and breaking out of the enclosing block.

This is a followup to #103981