Merge #8624

Merge #8624

8624: Automatically detect rust library source file map  r=vsrs a=vsrs

This PR adds a new possible `rust-analyzer.debug.sourceFileMap` value:
```json
{
    "rust-analyzer.debug.sourceFileMap": "auto"
}
```

I did not make it the default because it uses two shell calls (`rustc --print sysroot` and `rustc -V -v`). First one can be slow (https://github.com/rust-lang/rustup/issues/783)

Fixes #8619

Co-authored-by: vsrs <vit@conrlab.com>