Converting from UTF-8 to UTF-16 could have resulted in a buffer overflow if the buffer size was exactly the length of the converted string.
Pass string_view/span to convert_from/to_fs instead, and ensure the buffer is terminated. This replaces passing a pointer to the buffer and the buffer size as separate parameters, allowing the compiler to pass both in one parameter.
Removes use of `lengthof()`.
e2a796dbcd