Rollup merge of #77194 - pickfire:patch-7, r=withoutboats

Add doc alias for iterator fold

fold is known in python and javascript as reduce,
not sure about inject but it was written in doc there.

This was my first confusion when coming into rust, I somehow cannot find where is reduce, sometimes I still forget that it is known as `fold`.

Author: RalfJung

library/core/src/iter/traits/iterator.rs

@@ -1976,6 +1976,8 @@ pub trait Iterator {
     /// // they're the same
     /// assert_eq!(result, result2);
     /// ```
+    #[doc(alias = "reduce")]
+    #[doc(alias = "inject")]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     fn fold<B, F>(mut self, init: B, mut f: F) -> B