some SkAtomics cleanup

 - Replace sk_memory_order with std::memory_order.
 - Remove SkAtomic<T>.

SkPath was the only user of SkAtomic<T>, for its fConvexity and
fFirstDirection fields.  I've replaced them with std::atomic types, and
funneled access to them through methods that enforce the relaxed memory
order like SkAtomic<T> did.

For fConvexity, we can use the exisiting setConvexity() and
getConvexityOrUnknown() methods, adding a private const setConvexity()
to mutate convexity from const methods.  For fFirstDirection I've added
private setFirstDirection() and getFirstDirection() methods.

Removing SkAtomic<T> means SkAtomics.h no longer needs SkNoncopyable.h.
I've had to update a bunch of other headers that were depending on
transitive inclusion.

Change-Id: Ib238be71a121519db6e970a9a8955834e1298c87
Reviewed-on: https://skia-review.googlesource.com/c/174220
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
12 files changed