Zig toolchain uses slow-path for string shuffling in a few places

[fwsGonzo]

The ABI of the libc++ std::string is complex and hasn't been implemented host-side, so the current guest ABI for std::string uses a simple fallback method. It's probably better to first get the size() and the use something like https://en.cppreference.com/w/cpp/string/basic_string/resize_and_overwrite to initialize it.

[fwsGonzo]

I have considered just always allocating the long string variation of libc++ std::string, even when they are smaller.
Implementation details: https://joellaity.com/2020/01/31/string.html

The raw struct:

struct __long {
    size_type __cap_;
    size_type __size_;
    pointer __data_;
};