This adds the drmbuf format as a parameter separate from the obs texture
format that will be used. drmbuf's may have a variety of formats that we
need to pass correctly to get a usable texture which may correspond to
multi-platform texture formats.
DMA-BUF is a widespread Linux buffer sharing mechanism. It is what's
commonly used zero-copy screen sharing by Wayland compositors.
Add a new 'device_texture_create_from_dmabuf' vfunc to gs_exports,
and stub implementations to libobs-opengl. Add a new public method
gs_texture_create_from_dmabuf() that calls this vfunc.
Move the GLX-related code to gl-x11-glx, and introduce gl-nix as
a winsys-agnostic abstraction layer. gl-nix serves as the runtime
selector of which winsys going to be used. Only the X11/GLX winsys
is available now, but later commits will introduce the X11/EGL
winsys as well.
The gl-nix code was originally written by Jason Francis <cycl0ps@tuta.io>
This is in preparation for the future abstraction layer (gl-x11-*)
and also to match the actual name of the windowing system. When
running under X11, we can glue OpenGL through GLX or EGL, so the
new file name matches that now.
