Stabilise const_array_each_ref.

[bjoernager]

Tracking issue: #133289

This PR stabilises the items locked behind the const_array_each_ref feature gate:

impl<T, const N: usize> [T; N] {
    pub const fn each_ref(&self) -> [&T; N];

    pub const fn each_mut(&mut self) -> [&mut T; N];
}

As of writing, FCP is still pending for the feature.

@rustbot label +T-libs-api -T-libs

r? libs-api

[bjoernager]

@rustbot label -T-libs

[CosminPerRam]

Hey, I was just browsing stabilization PRs, isn't this the same as #143383?
Sorry if I'm mistaken.

[bjoernager]

It sure seems like it.