Update SkJPEGImageEncoder

(1) Use libjpeg-turbo color space extensions when possible.
(2) Use transform_scanline_procs when pre-libjpeg-turbo transformation
    are required.
(3) Add support for Gray and F16.

BUG=skia:

Change-Id: I77b977cb8c9e0afc17d907dd73a1cf3f16539bcc
Reviewed-on: https://skia-review.googlesource.com/7642
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
3 files changed