This makes more sense; we're updating the device, not the plugin itself.
This also means we don't need to funnel everything through callbacks like
GFileProgressCallback and we can also update the state without adding an
explicit callback to each derived device type.
It's actually less scary to see a SHA1 hash than it is to see a path like
/sys/devices/pci0000:00/0000:00:1d.0/usb1/1-1/1-1.2. It's also way easier to
copy and paste into the various fwupdmgr command that require a device ID and
also means we can match a partial prefix much like git allows.
If we also move to a model where plugins can be changed during different stages
of the update (e.g. during detach) then the device might change connection type
and then the sysfs path not only becomes difficult to paste, but incorrect.
Session software doesn't care about the format of the device ID (it is supposed
to be an implementation detail) and so there's no API or ABI break here. A few
plugins also needed to be ported, but nothing too worrying.
