Rollup merge of #92071 - ajtribick:patch-1, r=the8472

Update example code for Vec::splice to change the length

The current example for `Vec::splice` illustrates the replacement of a section of length 2 with a new section of length 2. This isn't a particularly interesting case for splice, and makes it look a bit like a shorthand for the kind of manipulations that could be done with a mutable slice.

In order to provide a stronger example, this updates the example to use different lengths for the source and destination regions, and uses a slice from the middle of the vector to illustrate that this does not necessarily have to be at the beginning or the end.

Resolves #92067

library/alloc/src/vec/mod.rs

@@ -2683,11 +2683,11 @@ fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
     /// # Examples
     ///
     /// ```
-    /// let mut v = vec![1, 2, 3];
-    /// let new = [7, 8];
-    /// let u: Vec<_> = v.splice(..2, new).collect();
-    /// assert_eq!(v, &[7, 8, 3]);
-    /// assert_eq!(u, &[1, 2]);
+    /// let mut v = vec![1, 2, 3, 4];
+    /// let new = [7, 8, 9];
+    /// let u: Vec<_> = v.splice(1..3, new).collect();
+    /// assert_eq!(v, &[1, 7, 8, 9, 4]);
+    /// assert_eq!(u, &[2, 3]);
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[inline]