Rollup merge of #87690 - sharnoff:mut-ptr-allocated-obj-link, r=Mark-Simulacrum

Add missing "allocated object" doc link to `<*mut T>::add`

The portion of the documentation expecting the link was already there, but it was rendered as "[allocated object]". The added reference is just copied from the documentation for `<*const T>::add`.

Author: camsteffen

library/core/src/ptr/mut_ptr.rs

@@ -596,6 +596,7 @@ impl<T: ?Sized> *mut T {
     /// enables more aggressive compiler optimizations.
     ///
     /// [`wrapping_add`]: #method.wrapping_add
+    /// [allocated object]: crate::ptr#allocated-object
     ///
     /// # Examples
     ///