Add missing features to the API

[TurkeyMan]

Add missing functionality to API.
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

[dlang-bot]

Thanks for your pull request and interest in making D better, @TurkeyMan! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20107	enhancement	core.atomic : Memory order is missing keys

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "master + druntime#2747"