Unify error reporting for intra-doc links

[jyn514]

Right now there are two places that deal with disambiguators:

1. The one I wrote in Disallow linking to items with a mismatched disambiguator #75079:

   rust/src/librustdoc/passes/collect_intra_doc_links.rs

   Line 782 in f5d7848

   let help_msg = format!("to link to the {}, use its disambiguator", kind.descr(id));

2. rust/src/librustdoc/passes/collect_intra_doc_links.rs

   Line 1138 in f5d7848

   &format!("to link to the {}, {}", res.descr(), action),

   
   which @euclio wrote in refactor and reword intra-doc link errors #74528. I didn't notice the second one even though I reviewed refactor and reword intra-doc link errors #74528 🙈.

It would be great to unify these into one function so the errors reported are consistent; I ran into some trouble with this in #75815 (comment).

[jyn514]

Now that I think about this, maybe this should be fixed before #75756 gets merged ...