ext/intl: migrate C code to C++ step 3.

[devnexen]

No description provided.

[bukka]

What's the actual reason for all of this?

[devnexen]

couple of reasons :
1/ icu C++ api is the main api, C wrappers versions of new features come later (when they do).
2/ mixing C++ with cumbersome procedural C makes the code more complicated (esp. memory management,e.g. zend mm and C++ objects, lesser chances of leaks).
3/ no more need to export C++ symbols as C.
4/ C++ has stronger typing, can be annoying again to mix with C "looseness".

[bukka]

It seems like it cought up from the https://unicode-org.github.io/icu-docs/apidoc/released/icu4c/ . It's just few things missing from that list.

But if you really think it's worth the time and can bring some significant features / reduce number of bugs then I will leave it up to you.

[bukka]

One thing to note is that it would be good to still keep it understandable for C developers and not try to introduce some C++ features just for the sake of it. I don't have personally have problem to understand C++ which I guess was the reason why the extension was written in really C way.

[bukka]

That comment was more about type of changes in #19429 rather than this though.