Converts bytes whose unsigned value is interpreted as Unicode code point (i.e. U+0000 to U+00FF, inclusive) to UTF-8 with potentially insufficient output space.
Returns the number of bytes read and the number of bytes written.
If the output isn't large enough, not all input is consumed.
Note that this function may write garbage beyond the number of bytes
indicated by the return value, so using a
&mut str interpreted as
&mut [u8] as the destination is not safe. If you want to convert into
&mut str, use
convert_utf16_to_str() instead of this function.