Un-hide iter::repeat_n

Author: scottmcm

library/core/src/iter/sources/repeat_n.rs

@@ -59,7 +59,6 @@ use crate::num::NonZeroUsize;
 /// ```
 #[inline]
 #[unstable(feature = "iter_repeat_n", issue = "104434")]
-#[doc(hidden)] // waiting on ACP#120 to decide whether to expose publicly
 pub fn repeat_n<T: Clone>(element: T, count: usize) -> RepeatN<T> {
     let mut element = ManuallyDrop::new(element);