feat: better handling of sorting/grouping files by extension

I'm currently using:
```bash
eza -a -1 -l -g --icons=never --color-scale=age --group-directories-first --time-style='\''+%Y-%m-%d %H:%M'\'' --git --total-size -F never
```

However, I would like to sort and order as follows:
- [x] directories first
- [x] dot files second
- [ ] files according to extensions (3rd)

So I am not able to get the remainder of the files grouped according their extension after having used the above.

Is this already possible?

If not, please add it as a feature improvement.

Start by reproducing the issue with the provided eza command and inspect how its sorting and grouping options are handled. Determine how directories and dot files should interact with extension grouping; done means the remaining files are grouped by extension while the requested directory-first and dot-file ordering remains intact.

Written by the indexing model from the issue text.