[sfnt] Implement 'COLR' v1 sweep gradients.

* freetype.h (FT_PaintSweepGradient): Add `FT_PaintSweepGradient` to
represent a 'COLR' v1 sweep gradient.
Update format.
(FT_PaintFormat): Update shifted paint formats.
Sync with spec.
* sfnt/ttcolr.c (read_paint): Logic to parse sweep gradients.
Fix struct access in radial gradient implementation.
3 files changed