[sfnt] Support variable 'COLR' v1 color lines.
* include/freetype/ftcolor.h (FT_ColorStopIterator): Add field
`read_variable` to indicate whether a variation index base should be read.
* src/sfnt/ttcolr.c: (FT_PaintFormat_Internal): New enumerations
`FT_COLR_PAINTFORMAT_INTERNAL_VAR_LINEAR_GRADIENT`
`FT_COLR_PAINTFORMAT_INTERNAL_VAR_RADIAL_GRADIENT`, and
`FT_COLR_PAINTFORMAT_INTERNAL_VAR_SWEEP_GRADIENT`.
(read_color_line): New parameter `read_variable`; update callers.
(read_paint): Handle new enumerations.
2 files changed
