Auto merge of #75916 - jyn514:unify-error-reporting, r=euclio

 Unify error reporting for intra-doc links

- Give a suggestion even if there is no span available
- Give a more accurate description of the change than 'use the
disambiguator'
- Write much less code

Closes #75836.
r? @euclio
cc @pickfire - this gets rid of 'disambiguator' like you suggested in https://github.com/rust-lang/rust/pull/75079#discussion_r464464195.