Auto merge of #12406 - MarcusGrass:fix-duplicate-std-instead-of-core, r=Alexendoo

Dedup std_instead_of_core by using first segment span for uniqueness

Relates to #12379.

Instead of checking that the paths have an identical span, it checks that the relevant `std` part of the path segment's span is identical. Added a multiline test, because my first implementation was worse and failed that, then I realized that you could grab the span off the first_segment `Ident`.

I did find another bug that isn't addressed by this, and that exists on master as well.

The path:
```Rust
use std::{io::Write, fmt::Display};
```

Will get fixed into:
```Rust
use core::{io::Write, fmt::Display};
```

Which doesn't compile since `io::Write` isn't in `core`, if any of those paths are present in `core` it'll do the replace and cause a miscompilation. Do you think I should file a separate bug for that? Since `rustfmt` default splits those up it isn't that big of a deal.

Rustfmt:
```Rust
// Pre
use std::{io::Write, fmt::Display};
// Post
use std::fmt::Display;
use std::io::Write;
```
---

changelog: [`std_instead_of_core`]: Fix duplicated output on multiple imports

0 files changed, 0 insertions, 0 deletions