This patches rewrites the GPU shaders of curve nodes for easier future development. This is a non-functional change. The new code avoids code duplication by moving common code into BKE curve mapping functions. It also avoids ambiguous data embedding into the gradient vectors that are passed to vectors and reduces the size of uniforms uploaded to the shader by avoiding redundancies. This is needed in preparation for the viewport compositor, which will utilize and extend this implementation. Reviewed By: fclem Differential Revision: https://developer.blender.org/D14689