6771: Properly attach inner attributes in Attrs::new r=matklad a=Veykril
Properly attach inner and outer attributes to the things they actually belong to in the HIR. ~~I can add some tests for this if wanted once I know where to put them/how to test for this.~~ Put some tests into `hover.rs`.
So the following snippet
```rust
mod foo {
//! Hello
}
```
now shows `Hello` on hover 🎉Fixes#2148
Co-authored-by: Lukas Wirth <lukastw97@gmail.com>
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