Rollup merge of #126140 - eduardosm:stabilize-fs_try_exists, r=Amanieu

Rename `std::fs::try_exists` to  `std::fs::exists` and stabilize fs_try_exists

FCP completed in tracking issue.

Tracking issue: rust-lang/rust#83186

Closes rust-lang/rust#83186

Stabilized API:

```rust
mod fs {
    pub fn exists<P: AsRef<Path>>(path: P) -> io::Result<bool>;
}
```

Author: matthiaskrgr