Copy skcms_internal header into src directory.

This CL should land after Skia's http://review.skia.org/774156,
which sets up placeholder files and Bazel rules which include
the new header. After these land and roll, the top-level header
and its references can be cleaned up and deleted.

Moving the header into src/ is useful because it needs to be
#included from `skcms_Transform.cc`. Using ..-relative #includes
in Google3 (i.e. `#include "../skcms_internal.h"`) seems dangerous
to me, so this CL lets us use `#include "skcms_internal.h"` instead.

The name is changed to "skcms_internals" from "skcms_internal" in
order to work around a Gerrit check for duplicated header names.

Change-Id: I4f6710be815f92d82d4d7a56c0cc326aed323910
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/774077
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Herb Derby <herb@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
8 files changed