Rollup merge of rust-lang#144054 - jsimmons:stabilize-as-array-of-cells, r=tgross35

Stabilize as_array_of_cells

This PR stabilizes

```rust
impl<T, const N: usize> Cell<[T; N]> {
    pub const fn as_array_of_cells(&self) -> &[Cell<T>; N];
}
```

Stabilization report: rust-lang#88248 (comment)
Closes: rust-lang#88248

Author: jhpratt

library/core/src/cell.rs

@@ -698,14 +698,14 @@ impl<T, const N: usize> Cell<[T; N]> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(as_array_of_cells)]
     /// use std::cell::Cell;
     ///
     /// let mut array: [i32; 3] = [1, 2, 3];
     /// let cell_array: &Cell<[i32; 3]> = Cell::from_mut(&mut array);
     /// let array_cell: &[Cell<i32>; 3] = cell_array.as_array_of_cells();
     /// ```
-    #[unstable(feature = "as_array_of_cells", issue = "88248")]
+    #[stable(feature = "as_array_of_cells", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "as_array_of_cells", since = "CURRENT_RUSTC_VERSION")]
     pub const fn as_array_of_cells(&self) -> &[Cell<T>; N] {
         // SAFETY: `Cell<T>` has the same memory layout as `T`.
         unsafe { &*(self as *const Cell<[T; N]> as *const [Cell<T>; N]) }

tests/ui/rfcs/rfc-1789-as-cell/from-mut.rs

@@ -1,7 +1,5 @@
 //@ run-pass
 
-#![feature(as_array_of_cells)]
-
 use std::cell::Cell;
 
 fn main() {