Replace dependencies on aged_containers

[scottschurr]

Issue Description

The collection of aged_containers (see src/ripple/beast/container) are STL-like containers that track the relative age of their contents. The aged_containers are specific to rippled, which means that they are maintained locally. The fact that they are STL-like carries with it all of the associated complexity.

The amount of complexity and maintenance risk that the aged_containers carries is not justified by the role they fill in the rippled code base. We should find std:: (preferable) or boost:: replacements for all uses of the aged_containers in the rippled code base, even if that means incurring some performance penalties. Once all uses of the aged_containers have been replaced, then we should remove the aged_container source code.

[nbougalis]

Alternatively, we should consider whether submitting them for inclusion in Boost makes sense. I know that this would require extra effort on our part, unless someone else is willing to adopt them and push them through Boost review.

[scottschurr]

If Mr. V wants to adopt them I'd be fine with that. But I doubt anyone on this team wants to adopt them thoroughly enough to get them through the Boost review process. I tried doing that once years ago with a small utility that I wrote (and was not accepted). The Boost review process can be brutal.

[intelliot]

@scottschurr do you still think this is worth doing?

[scottschurr]

Yes, removing the aged_containers from the code base is still very much worth doing. They are very complicated. They have already broken a couple of times as we have moved from one C++ Standard to the next. Fortunately @HowardHinnant was able to figure out fixes. They should be replaced with standard boost (or other library) functionality that someone (other than XRP Ledger developers) is maintaining.

The aged_containers are technical debt at its finest.

[scottschurr]

Case in point: https://github.com/XRPLF/rippled/pull/4486

[intelliot]

• there may be a boost option to consider - Boost Multi-index?
  • would have to do the work of switching it over in order to confirm
  • may need 1-2 container solutions - and it will harm performance. but maybe the perf cost isn't too high.
• is there a folly or abseil option?
  • we have an indirect dependency on abseil (but google sometimes doesn't maintain old versions of things)
  • google only maintains recipes for ~2 yrs or so
  • the folly available in conan is too old (and there's likewise no guarantee facebook will maintain it going forward)
  • could easily fork the recipe like we are with snappy
  • if folly hasn't changed their build process, it may be as easy as setting the commit hash you want
• conan makes it easier to add dependencies and update them
• may be useful to delete the oldest data without doing an expensive search
• should try to find a solution to the problem that has a maintainer
• no one has an objection to finding a replacement.
  • but for the time being, if issues crop up with the current implementation, @seelabs can maintain