This adds an unbuildColrV1 which does the inverse of colorLib.builder.buildColrV1.
Takes a LayerV1List and BaseGlypV1List and returns a map of base glyphs to raw data structures (list, dict, float, str, etc.).
Useful not only for debugging purpose, but also for implementing COLRv1 subsetting (where we need to drop whole chunks of paints which may be reused by multiple glyphs).