Stabilize const Atomic*::into_inner
Partial stabilization for https://github.com/rust-lang/rust/issues/78729, for which the FCP has already completed.
The other `into_inner` functions in that tracking issue (`UnsafeCell`, `Cell`, `RefCell`) are blocked on https://github.com/rust-lang/rust/issues/73255 for now.
```console
error[E0493]: destructor of `UnsafeCell<T>` cannot be evaluated at compile-time
--> library/core/src/cell.rs:2076:29
|
2076 | pub const fn into_inner(self) -> T {
| ^^^^ the destructor for this type cannot be evaluated in constant functions
2077 | self.value
2078 | }
| - value is dropped here
```
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