tweak and clean up conversion to perceptual space

- try ITU-R BT.2020 YPbPr conversion instead of ITU-R BT.601 as seems
  to do slightly better on specular highlights plus it's so hip and
  cutting edge
- remove spurious luminance added in when doing chroma differential,
  which was a mystery residual of CIELab
- don't need anything from common/colorspaces.h any more
1:1 view demosaicer fixups

This fixes #9388, which applies to all sensors -- make 1:1 view use
chosen demosaicer in mid-quality config.

Update demosaic plugins/darkroom/demosaic/quality conf to mention VNG
in longdescription as x-trans' PPG equivalent. This leaves the config
choice inaccurate for x-trans, but at least doesn't break exsiting
configs. (If change this message to "at most PPG/VNG (reasonable)" then
demosaic will still do the right thing with exiting configs, but the
preferences screen will show a blank entry for this choice
until the user next changes it.)
x-trans demosaic fixups

- give up interpolation on failed malloc
- use dt's CLAMPS
- allocate Markesteijn buffers in a block outside of parallel
  construct to avoid many alloc/free cycles
inpaint highlight reconstruction for x-trans
fix-up noisy Markesteijn demosaic borders
first pass at rawspeed for x-trans

- update dngmeta.sh to read 6x6 CFA -- this code could also work for
  2x2 CFAs, though currently each has its own path
- patch rawspeed to handle 14 bpp RAF files -- this may not work in
  all cases, needs more testing
- pre-rotate matrix when load image, as with libraw code
- add X100S support in cameras.xml

White/black levels and crop may differ from libraw version.
rawspeed support for rest of fuji x-series

Conflicts:
	tools/dngmeta.sh
allow for compile-time disabling of x-trans code
document different behavior for x-trans sensors
revise x-series crops for rawspeed

use crops as reported in raw file rather than from observation