lookingGlass: Handle unprintable object

lookingGlass: Handle unprintable object

We currently throw an error when encountering a result that cannot
be represented as string, with the prompt appearing somewhat stuck
(the input cannot be committed).

Showing a lame fallback instead at least avoids that issue. When
the object has a typeof 'object' but is not an instanceof Object,
we are likely dealing with an ES module, and can show a slightly
less lame fallback.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2842>