Currently, obs-nix.c is highly tied to the X11 display
server. It includes X11 headers directly, and make use
of X11 functions. Most of the code inside obs-nix.c that
is X11-specific is related to hotkeys handling.
Introduce a new vtable for hotkeys callbacks, that will
used by X11 and Wayland to expose their specific routines.
In this commit, only the X11 hotkeys vtable is implemented.
Move all the X11-specific code to obs-nix-x11.c, and add
a new function to retrieve the X11 hotkeys vtable.
Georges Basile Stavracas Neto