[colorLib] More optimized LayerList builder

[behdad]

Currently the code adds base paints to the layer list in order of the glyph index. It would share better if it did that by decreasing number of layers. The code is in buildColrV1:

    for baseGlyph, paint in colorGlyphItems: 
        try: 
            baseGlyphs.append(buildBaseGlyphPaintRecord(baseGlyph, layerBuilder, paint)) 
    
        except (ColorLibError, OverflowError, ValueError, TypeError) as e: 
            errors[baseGlyph] = e