Rollup merge of rust-lang#147489 - chenyukang:yukang-prefer-repeat-n, r=Kivooeo,oli-obk

Prefer to use repeat_n over repeat().take()

More from rust-lang#147464, but batch processed with `ast-grep` to find and replace.

second commit add notes for library: rust-lang@affaf53

r? ``@RalfJung``

Author: Zalathar

core/src/iter/sources/repeat.rs

@@ -8,13 +8,17 @@ use crate::num::NonZero;
 /// Infinite iterators like `repeat()` are often used with adapters like
 /// [`Iterator::take()`], in order to make them finite.
 ///
+/// If you know the number of repetitions in advance, consider using [`repeat_n()`]
+/// instead, as it is more efficient and conveys the intent more clearly.
+///
 /// Use [`str::repeat()`] instead of this function if you just want to repeat
 /// a char/string `n` times.
 ///
 /// If the element type of the iterator you need does not implement `Clone`,
 /// or if you do not want to keep the repeated element in memory, you can
 /// instead use the [`repeat_with()`] function.
 ///
+/// [`repeat_n()`]: crate::iter::repeat_n
 /// [`repeat_with()`]: crate::iter::repeat_with
 /// [`str::repeat()`]: ../../std/primitive.str.html#method.repeat
 ///