Handling of relative path URL

### Describe the bug

According to rfc 8089 paths for file URIs are absolute. ``yarl.URL`` does not complain about them but displays a wrong repr.

### To Reproduce

1. yarl 1.7.2
2. Instantiate file URL with "relative" path (see below)

### Expected behavior

``yarl.URL('file:foo/bar')`` should raise exception or produce instance with correct repr: ``assert repr(URL('file:foo/bar')) == 'file:foo/bar'``

### Logs/tracebacks

```python-traceback
In [1]: from yarl import URL

In [2]: URL('file:foo/bar') == URL('file:///foo/bar')
Out[2]: False

In [3]: URL('file:///foo/bar')
Out[3]: URL('file:///foo/bar')

In [4]: URL('file:foo/bar')
Out[4]: URL('file:///foo/bar')

In [5]: URL('file:foo/bar').path
Out[5]: 'foo/bar'

In [6]: URL('file:///foo/bar').path
Out[6]: '/foo/bar'
```
```

### Python Version

```console
$ python --version
3.8.12
```

### multidict Version

```console
$ python -m pip show multidict
5.1.0
```

### yarl Version

```console
$ python -m pip show yarl
1.7.2
```

### OS

NixOS

### Additional context

_No response_

### Code of Conduct

- [X] I agree to follow the aio-libs Code of Conduct