Move Vec class into header.

This is a first step for creating separate translation units for
the Transform code. This CL introduces a `skcms_private` namespace
for symbols which will need to cross the boundary between skcms.cc
and Transform.

Change-Id: I8f52e9e60524e95a2302d1a279d19793680d755d
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/773060
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
3 files changed