RenderEngine API: add viewport draw utility functions to bind a GLSL fragment

shader for converting colors from linear to display space, based on the scene
color management settings.

if engine.support_display_space_shader(scene): # test graphics card support
	engine.bind_display_space_shader(scene)
	# draw pixels ..
	engine.unbind_display_space_shader()

intern/opencolorio/fallback_impl.cc

@@ -381,6 +381,11 @@ void FallbackImpl::matrixTransformScale(float * , float * , const float *)
 {
 }
 
+bool FallbackImpl::supportGLSLDraw(void)
+{
+	return false;
+}
+
 bool FallbackImpl::setupGLSLDraw(struct OCIO_GLSLDrawState **state_r, OCIO_ConstProcessorRcPtr *processor, bool predivide)
 {
 	return false;