For the prefs command, we first fetch the extension info to check
whether the extension exists and actually has preferences. This
pattern can be useful for other commands and properties, so split
out a generic helper function.
https://gitlab.gnome.org/GNOME/gnome-shell/issues/2391
Error reporting is useful when used interactively, but often undesirable
when used in scripts. Account for that with a common --quiet option,
which is more convenient than redirection stderr to /dev/null.
https://gitlab.gnome.org/GNOME/gnome-shell/issues/2391
The gnome-extensions tool code is really independent from the rest of the
code base, and could be used either as part of the gnome-shell build or as
stand-alone project (for example for the extension-ci docker image).
We can actually support both cases by moving the code to a subproject.
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/877
