Renovate core.atomic, improve and simplify the constraints on functions.

Most functions are slightly more efficient.
Concentrate more specific work into less surface area.

Fixes Issue 20107 - core.atomic : Memory order is missing keys
Fixes Issue 20106 - core.atomic : atomicFence doesn't accept MemoryOrder
Fixes Issue 20105 - core.atomic 'cas' function is incomplete
Fixes Issue 15007 - core.atomic match C++11
Fixes Issue 8831 - core.atomic: add compare-and-swap function with other result type