Since the corresponding source files do not include "config.h", and are
not compiled with `GTK_COMPILATION`, they will generate the wrong symbol
exporting under Windows.
Add adds a demo showing off GskGLShaderNode in various ways.
It has a transistion widget, using some examples from
gl-transitions.com, with child widgets being both images, a GL area
and real widgets (that let you edit the transition shaders
themselves.
It also has a fancy fire effect on hove on the buttons.