OpenGL ES 3.1 introduces compute shaders. This patch enables them also
in QOpenGLShader/QOpenGLShaderProgram.
A GL/GLES example using QOpenGLShaderProgram for compute shaders is also
included.
Change-Id: I3951a302d7c2b096548f829b9b4578b5a525c453
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>