/// Converts a UTF-8 string slice into a null-terminated UTF-16 encoded buffer.
///
/// # Parameters:
///
/// - `const NSTDStr *str` - The UTF-8 encoded string slice.
///
/// # Returns
///
/// `NSTDOptionalVec utf16` - The new UTF-16 encoded buffer on success, or an uninitialized "none"
/// variant on error.
///
/// # Safety
///
/// `str`'s data must be valid for reads, especially in terms of UTF-8 conformance.
NSTDAPI NSTDOptionalVec ;