Fix atomic_ref<16 bytes>::is_always_lock_free

[AlexGuteniev]

Fixes #4472

• Invent always-lock-free compile-time check independently from atomic<T>
  • Sharing the checks implementation is a bomb for vNext. In vNext I expect atomic<3 bytes> to be always-lock-free, but not atomic_ref<3 bytes>
  • Having the template constant in global scope is unnecessary, atomic_ref<T> doesn't have volatile things
• Expand test matrix for that
  • Requires DCAS machine, but it is Win8+ requirement
  • clang-cl wants cx16 feature enabled for that

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[StephanTLavavej]

☢️ 🛠️ 😻