Tracking Issue for feature(pin_static_ref): Pin::{static_ref,static_mut}

Tracking issue for `#![feature(pin_static_ref)]`, as added by #77726.

Interface:
```rust
impl<T: ?Sized> Pin<&'static T> {
    pub const fn static_ref(r: &'static T) -> Pin<&'static T>;
}

impl<T: ?Sized> Pin<&'static mut T> {
    pub const fn static_mut(r: &'static mut T) -> Pin<&'static mut T>;
}
```

@rustbot modify labels: +B-unstable +C-tracking-issue +T-libs