Rollup merge of #121082 - peterjoel:atomic-docs, r=cuviper

Clarified docs on non-atomic oprations on owned/mut refs to atomics

I originally misinterpreted the documentation to mean that the compiler can/will automatically optimise away atomic operations whenever the data is owned or mutably referenced.

On re-reading I think it is not technically incorrect, but specifically mentioning _how_ the atomic operations can be avoided also prevents this misunderstanding.

library/core/src/sync/atomic.rs

@@ -27,8 +27,9 @@
 //! Rust atomics currently follow the same rules as [C++20 atomics][cpp], specifically `atomic_ref`.
 //! Basically, creating a *shared reference* to one of the Rust atomic types corresponds to creating
 //! an `atomic_ref` in C++; the `atomic_ref` is destroyed when the lifetime of the shared reference
-//! ends. (A Rust atomic type that is exclusively owned or behind a mutable reference does *not*
+//! ends. A Rust atomic type that is exclusively owned or behind a mutable reference does *not*
-//! correspond to an "atomic object" in C++, since it can be accessed via non-atomic operations.)
+//! correspond to an “atomic object” in C++, since the underlying primitive can be mutably accessed,
+//! for example with `get_mut`, to perform non-atomic operations.
 //!
 //! [cpp]: https://en.cppreference.com/w/cpp/atomic
 //!