XUASTC's next step: Intra-prediction of weight grids

Binomial has shown that image compression and GPU texture compression aren't separate fields . They're the same field, and the tools from one transfer directly to the other. XUASTC is currently using JPEG-style DCT (from 1992) on ASTC weight grids: https://github.com/BinomialLLC/basis_universal/wiki/XUASTC-LDR-Weight-Grid-DCT We ported JPEG-style coding into ASTC, even preserving how libjpeg-style…