It's possible to configure `sort_mode` for the project panel like that:

```json
"project_panel": {
"sort_mode":"directories_first"
}
```

However, `workspace: open files` doesn't respect this setting and always
shows files and directories mixed. This change fixes the issue.

Release Notes:

- Improved sorting in `workspace: open files`

---------

Co-authored-by: Christopher Biscardi <chris@christopherbiscardi.com>