Improve discoverability of memory interface docs

[Tokazama]

Looking at some of the more recent changes and found that a lot of stuff is documented somewhere but not always in a discoverable way. For example, the doc string for AtomicMemory mentions the following without any of them being directly documented.

• Core.CPU
• getindex_atomic
• setindex_atomic!
• setindexonce_atomic!
• swapindex_atomic!
• modfiyindex_atomic!
• replaceindex_atomic!

Since these all inevitably make it into a public interface and are mentioned in doc strings it would make sense for them to have their own doc strings and be marked as public.

For Core.CPU the explanation in GenericMemory's doc string seems sufficient. With some digging you can find some extra info in the atomic related macros for the others, but I'm not sure if there's a more complete interface outside of the documented macros.

Edit: I've reported some other missing docs recently with the advent of public but I continue to find them semiregularly (just remembered Base.RefValue). Would it be more efficient to have an issue pinned with a list of internals discussed for being made public and documented? Then these could be linked to relevant PRs and issues. This would make contributing on this front a lot easier.

[Seelengrab]

Possible dup of #46739 , but at the very least this is related.

[jakobnissen]

IIUC, all the atomic functions's functionality can be achieved with the documented macros @atomic, @atomiconce, @atomicswap, and @atomicreplace. Perhaps the documentation for AtomicMemory should just mention the macros and not the functions, and the functions are supposed to be internal?

[Seelengrab]

Well how should one implement memories making use of these functions without them being documented? These aren't the intrinsics they're built on, or am I mixing things up? 🤔

[Tokazama]

I'm pretty sure there will need to be some overloading for array wrappers.