`impl RefUnwindSafe` for `&T` and `&mut T` is missing from documentation

### Location

https://doc.rust-lang.org/nightly/std/panic/trait.RefUnwindSafe.html

### Summary

The implementations of `RefUnwindSafe` for `&T` and `&mut T` are missing from the documentation.

This is weird as the `UnwindSafe` documentation includes the implementations for references and pointers, but `RefUnwindSafe` only has the pointer implementations listed.