Merge #836

836: auto_import: fix bug when the common path was shorter than both the c… r=matklad a=eulerdisk

Fix bug when the common path was shorter than both the current use and target path.

Wrong 1 (unnecessary self)
```
use std::fmt::nested::Debug;
std::fmt::Display<|>
```
--->
```
use std::fmt::{ self, Display, nested::Debug};
Display<|>
```

Wrong 2 (unnecessary, Debug disappear!!)
```
use std::fmt::Debug;
std::fmt::nested::Display
```
-->
```
use std::fmt::Debug::{ self, nested::Display, };
Display<|>
```

Co-authored-by: Andrea Pretto <eulerdisk@gmail.com>