Improve Shading Language Support in GraphicsFuzz

GraphicsFuzz is a tool that helps graphics driver makers capture defects by fuzzing and rendering semantically equivalent shaders. The tool applies the metamorphic testing technique that transforms shaders using the available functions in OpenGL shading language (GLSL). Currently, GLSL built-in functions are not fully supported by the tool. Providing a new set of GLSL features to GraphicsFuzz would create new ideas of transformation, and help the tool to detect a wider range of bugs.