Rollup merge of rust-lang#103996 - SUPERCILEX:docs, r=RalfJung

Add small clarification around using pointers derived from references

r? `@RalfJung`

One question about your example from rust-lang/libs-team#122: at what point does UB arise? If writing 0 does not cause UB and the reference `x` is never read or written to (explicitly or implicitly by being wrapped in another data structure) after the call to `foo`, does UB only arise when dropping the value? I don't really get that since I thought references were always supposed to point to valid data?

```rust
fn foo(x: &mut NonZeroI32)  {
  let ptr = x as *mut NonZeroI32;
  unsafe { ptr.cast::<i32>().write(0); } // no UB here
  // What now? x is considered garbage when?
}
```

Author: matthiaskrgr

library/core/src/ptr/mod.rs

@@ -35,7 +35,8 @@
 //!   be used for inter-thread synchronization.
 //! * The result of casting a reference to a pointer is valid for as long as the
 //!   underlying object is live and no reference (just raw pointers) is used to
-//!   access the same memory.
+//!   access the same memory. That is, reference and pointer accesses cannot be
+//!   interleaved.
 //!
 //! These axioms, along with careful use of [`offset`] for pointer arithmetic,
 //! are enough to correctly implement many useful things in unsafe code. Stronger guarantees
@@ -64,7 +65,6 @@
 //! separate allocated object), heap allocations (each allocation created by the global allocator is
 //! a separate allocated object), and `static` variables.
 //!
-//!
 //! # Strict Provenance
 //!
 //! **The following text is non-normative, insufficiently formal, and is an extremely strict