While we can now build gnome-extensions-tool as stand-alone project,
we are currently missing any translations, as those are part of
gnome-shell.
The easiest option for addressing this would be to symlink the toplevel
po directory into the subproject, however that would mean duplicating
the entire gnome-shell message catalogs.
So instead, set up a bare po directory and provide a script to populate
it from the translations in the toplevel po directory.
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/877
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
