Re-exports core::str::Utf16CodeUnits in std::str

Closes #17751

Author: Sawyer47

src/libcollections/str.rs

@@ -75,7 +75,7 @@ use vec::Vec;
 pub use core::str::{from_utf8, CharEq, Chars, CharOffsets};
 pub use core::str::{Bytes, CharSplits};
 pub use core::str::{CharSplitsN, AnyLines, MatchIndices, StrSplits};
-pub use core::str::{eq_slice, is_utf8, is_utf16, Utf16Items};
+pub use core::str::{Utf16CodeUnits, eq_slice, is_utf8, is_utf16, Utf16Items};
 pub use core::str::{Utf16Item, ScalarValue, LoneSurrogate, utf16_items};
 pub use core::str::{truncate_utf16_at_nul, utf8_char_width, CharRange};
 pub use core::str::{Str, StrSlice};