Genes are selfish.
esv::u32str_size - A function object to get the length of a u32 string: get the character counter.
Don't waste time on superfluous things.
The function object is the object of instantiated template class esv::str_size_class .
It gets string size by template type traits.
It gets string size by searching until '\0' is found.
It works on both string literal or string made by new.
For esv::str_size, type_xt is char; for esv::wstr_size, type_xt is wchar_t, ..., etc.