Add Waifu2x denoising

[Moelancholy]

There is currently no Waifu2x wrapper using vs-mlrt that allows the user to use the Waifu2x denoising. This can be useful for chroma reconstruction, or, in certain circumstances, for its denoising capabilities alone. Seeing as regress chroma_recon is already part of vs-denoise, it seems like one such wrapper would belong here.