avdevice/avfoundation: kCVPixelFormatType_OneComponent8 only exists from 10.8 onward

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/drawtext: Add basic text shaping using libfribidi

Fixes ticket #3758

Reviewed-by: Andrey Utkin <andrey.krieger.utkin@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>