This saves all the USB plugins from connecting to the context and managing the
device lifecycle and allows devices that uses FuUsbDevice to be removed
automatically.
This makes supported plugins *much* smaller indeed.
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.
This allows end-users testing a specific plugin to start fwupd with an extra
command line parameter, e.g. `--plugin-verbose=unifying` to output a lot of
debugging information to the console for that specific plugin.
This replaces a lot of ad-hoc environment variables with different naming
conventions.
