Rollup merge of rust-lang#85464 - steffahn:fix_ub_in_ptr_swap_docs, r=dtolnay

Fix UB in documented example for `ptr::swap`

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``@rustbot`` label T-doc T-libs

Author: RalfJung

library/core/src/ptr/mod.rs

@@ -342,10 +342,12 @@ pub const fn slice_from_raw_parts_mut<T>(data: *mut T, len: usize) -> *mut [T] {
 /// ```
 /// use std::ptr;
 ///
-/// let mut array = [0, 1, 2, 3];
+/// let mut array: [i32; 4] = [0, 1, 2, 3];
+///
+/// let array_ptr: *mut i32 = array.as_mut_ptr();
 ///
-/// let x = array[0..].as_mut_ptr() as *mut [u32; 3]; // this is `array[0..3]`
-/// let y = array[1..].as_mut_ptr() as *mut [u32; 3]; // this is `array[1..4]`
+/// let x = array_ptr as *mut [i32; 3]; // this is `array[0..3]`
+/// let y = unsafe { array_ptr.add(1) } as *mut [i32; 3]; // this is `array[1..4]`
 ///
 /// unsafe {
 ///     ptr::swap(x, y);