Create an iterator over the UTF-16 encoded codepoints in v, returning invalid surrogates as LoneSurrogates.

Example

use std::str;
use std::str::{ScalarValue, LoneSurrogate};

// 𝄞mus<invalid>ic<invalid>
let v = [0xD834, 0xDD1E, 0x006d, 0x0075,
         0x0073, 0xDD1E, 0x0069, 0x0063,
         0xD834];

assert_eq!(str::utf16_items(v).collect::<~[_]>(),
           ~[ScalarValue('𝄞'),
             ScalarValue('m'), ScalarValue('u'), ScalarValue('s'),
             LoneSurrogate(0xDD1E),
             ScalarValue('i'), ScalarValue('c'),
             LoneSurrogate(0xD834)]);