test_only.c overhaul

  - always print a curve per channel
  - Linear -> Identity
  - try to approximate skcms_TransferFunction with skcms_TF13
  - print all curve floats out at %.6g
  - get rid of for_unit_test

Change-Id: I8e7c7a8beba161594b06f8d1cecb43c22e7ef3f6
Reviewed-on: https://skia-review.googlesource.com/121488
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
43 files changed