Hi Alain,
Actually I wasn't aware that HE is capable to do this, before making that suggestion. Later I realized that it can be done already but it is a bit problematic for now. If you put a toolbar vertically between file explorer window and editor, it disappears in a mysterious way.

It directly goes to the far left of the main window and stays under the file explorer window. If you make file explorer auto hide, you will see that toolbar. In that position without opening file explorer drag the toolbar near editor window again and hope it to stay there

Then you can make file explorer docked again and now you managed to have an vertical toolbar

I think it will be solved soon since Alex took this to todo list.
Thanks...