Change the interface switcher widget

[brichet]

Problem

The interface switcher widget is currently a MenuBar widget (from Lumino) with only one first level item (Open with...).
The MenuBar widget catches the left and right arrow keys event, to move from one menu item to an other (in this case nothing happen since there is only one item).
This behavior breaks attempt to improve accessibility in toolbar by using arrow keys to navigate between items (jupyterlab/jupyterlab#15021 (comment)).

Proposed Solution

Using a select component, more appropriate for a toolbar.