Move SkOSPath out of include/core.

It is moved to src/utils. It is almost a tool, but has two uses in
src/ports.

The existing SkOSFile.cpp is left empty for the time being since it is
mentioned in Chromium's BUILD.gn for Skia.

Change-Id: I3bb7f7c4214359eb6ab906bfe76737d20bf1d6c7
Reviewed-on: https://skia-review.googlesource.com/4536
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Ben Wagner <bungeman@google.com>
27 files changed