We will use GUsb rather than libusb directly in the future. This should
simplify a lot of the integration work and changes such as supporting
hotplugging. It will also require quite a lot of internal changes.
libfprint already uses G_DEBUG_HERE in a lot of places which requires
GLib 2.50. Also add the appropriate defines so that usage of newer API
will result in warnings.
Instead of having to modify both fp_internal.h to list each driver
definition structure, and core.c to add those drivers to arrays we
can loop over, generate both of those using meson.
We shouldn't need to specifically enable debug logging to get useful
data out of a compiled libfprint either, so always enable debugging
output. It will still be switched off at runtime, by default.
There are no parts of libfprint that are so resource intensive that we'd
want to disable logging. This avoids (hopefully rare) cases where
compiled versions of libfprint are distributed with logging completely
disabled, and thus can't be debugged.
