[sfnt] Support 'COLR' v1 variable `PaintVarScale*`. * src/sfnt/ttcolr.c: (FT_PaintFormatInternal): New enumeration values `FT_COLR_PAINTFORMAT_INTERNAL_VAR_SCALE`, `FT_COLR_PAINTFORMAT_INTERNAL_VAR_SCALE_CENTER`, `FT_COLR_PAINTFORMAT_INTERNAL_VAR_SCALE_UNIFORM`, and `FT_COLR_PAINTFORMAT_INTERNAL_VAR_SCALE_UNIFORM_CENTER`. (read_paint): Handle new enumeration values.