The current code relies on GLib API and uses the
available mounts to calculate the available partition
size. This is because this code assumes that more
than one OS can be installed in the same drive, and
wouldn't make sense to show the whole disk size in
this situation.
That, however, clashes with the general purpose of
the panel, for it is meant to show general information
about the user's computer, and it is not reporting
the full disk size.
Fix that by using the UDisks API to get the real size
of the full disks.
https://bugzilla.gnome.org/show_bug.cgi?id=639376
Slighly modified by Iain Lane <iainl@gnome.org> to
port to meson and add udisks2 to CI deps.
Fixes#285.
Fixes#302.
2520aea647