rustdoc/stdlib docs: Auto trait implementations are missing reference types.

[alercah]

The auto traits Sync and RefUnwindSafe do not indicate anywhere in generated documentation that they are generated for reference types. The RefUnwindSafe page appears to not have any auto implementations listed; Sync's page lists auto implementors but does not include references. The reference page covers it in the prose, but neither of the traits appears in the implementation list.

[ExpHP]

I think it is not just references, but all primitive types; u8, (), [T], ...

Edit: Except the negative impls for *mut T and *const T, but those are explicitly in the source code of core.

[GuillaumeGomez]

Fixed by #50533.