os.expandTilde "~user" support
### Summary

`os.expandTilde` may support  `"~user"`, in addition to path beginning with `"~"`

### Description

Python's `os.path.expanduser` support both `'~'` and `'~user'`

And there's a TODO in source code of `os.expandTilde`:

```
    # TODO: handle `~bob` and `~bob/` which means home of bob
```

Also, if `~user` cannot be replaced, the path will be returned AS-IS.

### Alternatives

_No response_

### Examples

```nim
import std/os
echo os.expandTilde("~root")
```

### Backwards Compatibility

This is an expansion to the previous procedure.

A few path that didn't be expanded will be.

### Links

<https://docs.python.org/3/library/os.path.html#os.path.expanduser>

A todo in issue #8177 [make extractFilename("~bob") work](https://github.com/nim-lang/Nim/issues/8177#issue-337331114)