Rollup merge of #97366 - WaffleLapkin:stabilize_array_slice_from_ref, r=dtolnay

Stabilize `{slice,array}::from_ref`

This PR stabilizes the following APIs as `const` functions in Rust `1.63`:
```rust
// core::array
pub const fn from_ref<T>(s: &T) -> &[T; 1];

// core::slice
pub const fn from_ref<T>(s: &T) -> &[T];
```

Note that the `mut` versions are not stabilized as unique references (`&mut _`) are [unstable in const context].

FCP: https://github.com/rust-lang/rust/issues/90206#issuecomment-1134586665

r? rust-lang/libs-api `@rustbot` label +T-libs-api -T-libs

[unstable in const context]: https://github.com/rust-lang/rust/issues/57349

diff --cc library/core/src/slice/raw.rs
Simple merge