ZendMM C++ api

[devnexen]

Description

While working on intl migration to be fully in C++, I was thinking if we could provide a ZendMM C++ api instead of the actual C usage and, while it is not awful as is, we can use the opportunity to use templates instead of having to do super explicit casts.

e.g.

template<T, S = size_t> T ZendMM::fast_alloc(S len) {}

If it was only for intl, not sure that would be worth it but there is couple of C++ extensions out there.
(NB: Maybe reusing a subset of this old PR).

[devnexen]

forgot we re dealing with C++11 so we can reinforce more the "contract" even in the abscence of C++20 concepts.

template<T, S = size_t, typename = typename std::enable_if<
        std::is_integral<S>::value && std::is_unsigned<S>::value
    >::type> T ZendMM::fast_alloc(S len) {}

so we forbid "silly" usage with signed types :)

[devnexen]

Was toying around superficially with the idea with this "draft not to be merged", while it is feasible, it definitely needs a RFC.