Undo libosrm API break by adding old interface as method overload

[mjjbell]

Issue

Alternative to #5860

Removes the breaking libosrm API change by adding the old interface to the new. This does not introduce any new breaks.

The downside of this is that it allows for multiple ways to return JSON responses.

Tasklist

• CHANGELOG.md entry (How to write a changelog entry)
• add tests (see testing documentation
• review
• adjust for comments
• cherry pick to release branch

Requirements / Relations

Closes #5741
Closes #5548

[akashihi]

Just thinking loudly - can we use some template magic to avoid methods duplication?

[mjjbell]

Just thinking loudly - can we use some template magic to avoid methods duplication?

I'm not a templates expert, but with a bit of meta-programming it looks like we can do something like:

    template <class T,
              typename = std::enable_if_t<is_any<T, json::Object, engine::api::ResultT>::value>>
    Status Route(const engine::api::RouteParameters &params, T &result) const;

Is there a nicer way to do it? This feels a bit more difficult to understand than the overloaded methods, given osrm.hpp also acts as documentation.

[akashihi]

You meta-programming kung fu is better than mine :) Let's wait for a second opinion.