- Introduce ff_draw_init2, which takes explicit colorspace and range
  args
- Use lavu/csp and lavfi/colorspace for conversion, rather than the
  lavu/colorspace.h macros
- Use the passed-in colorspace when performing RGB->YUV conversions

The upshot of this is:
- Support for YUV spaces other than BT601
- Better rounding for all conversions
- Particular rounding improvements in >8-bit formats, which previously
  used simple left-shifts
- Support for limited-range RGB
- Support for full-range YUV in non-J pixfmts

Due to the rounding improvements, this results in a large number of
minor changes to FATE tests.
Signed-off-by: rcombs <rcombs@rcombs.me>