Previously the conversion mechanism called `std::string::c_str` and passed it to `String(cString:)` which accepts a null-terminated string. If the string contains a `\0` character, this failed to initialize the entire string properly.
This fixes a crash that happened when creating an instance of `std::string` from a `Swift.String` that contains non-ASCII characters.
When converted to a UTF-8 array, such characters might be represented by numbers that fall out of `CChar`'s boundaries if they have a sign bit set to 1. This is normal and shouldn't trigger a crash or an assertion failure.
This allows `std::string` to be constructed implicitly from a String literal, which is convenient e.g. when calling C++ APIs that take `std::string` as a parameter.
For some reason this isn't working, so I reverted to the previous approach. We can try to re-visit this in the future for a potential perf improvement.
This allows projects that don't want to pull in the entire C++ standard library to use stdlib-independent C++ interop utilities like `CxxSequence`.
This also makes the utilities available on platforms where we don't currently have the `std` overlay available, e.g. Windows.
