In qwerty_sdl.c the u_device_assign_xdev_roles function is used for
knowing which devices are being used by the user. These could
be other physical devices. And as such the idea of a default focused
device is introduced and depends upon which devices the user already
has. With this change qwerty devices should be properly introduced
to fill any device the user may not have.
It was necessary to add a list of xdevs to oxr_sdl2_hack_start and to
populate such list from its callees.
That includes sdl2_program.gui_program->xdevs which was not being filled
for the monado-service target.
The Qwerty driver will emulate an HMD and controllers through the use
of mouse and keyboard, and in particular, using the SDL key events
generated from the debug GUI.