Re-implement flatpak_installation_list_installed_refs_for_update() using
a FlatpakTransaction, so we can guarantee it always gives the same set
of things to update as the update command. This API is used by GNOME
Software and many times in the past g-s has not shown the same list of
apps to be updated as the flatpak CLI. See:
- https://gitlab.gnome.org/GNOME/gnome-software/issues/539
- https://gitlab.gnome.org/GNOME/gnome-software/-/merge_requests/430
This commit also expands the unit tests for this API, which were already
quite good. Now we test that missing subpaths of locale extensions show
up as updates, and updates that have been pulled but not deployed show
up as well. The latter is a break from how this function used to behave,
but it seems unlikely to break any application.
e847bb31b6