Let's use the sysfs path of the device to make sure we only load evdev
device, not legacy mousedev ones for instance. We rely on the sysfs
API/ABI guarantees and look for devices finishing by /input%d/event%d.
This backend is a event backend that can be enabled for EGL (for now).
It uses udev (gudev) to query input devices on a linux system, listens to
keyboard events from input devices and xkbcommon to translate raw key
codes into key keysyms.
This commit only supports key events, more to follow.