graphics/glx-utils: add new port

A few popular OpenGL X11 demos from Mesa:

• glxinfo prints capabilities of OpenGL driver
• glxgears draws rotating gears and prints FPS

Inspired by: D26077, glx-utils (CentOS, PkgSrc), glxinfo (AUR, MacPorts, Nix)
Motivated by: testing GLX on Xwayland, avoiding cruft and extra deps