Support scan script selection for progressive argument

[jarun]

This is a feature request. Apologies if it already exists and please direct me to the right option.

For the JPEG progressive option, the current code calls jpeg_simple_progression at

Pillow/src/libImaging/JpegEncode.c

Line 218 in fdbd719

jpeg_simple_progression(&context->cinfo);

Would it be possible to support an argument to specify the scan script to use?

[motioncircus]

This would be awesome. I have some 5K images, at @5MEG each that need to be viewable in the browser and multi scan progressive is the way to go, rather than starting at a creeping scanline.