Rollup merge of #109312 - petrochenkov:docice5, r=GuillaumeGomez

rustdoc: Cleanup parent module tracking for doc links

Keep ids of the documented items themselves, not their parent modules. Parent modules can be retreived from those ids when necessary.

Fixes rust-lang/rust#108501.
That issue could be fixed in a more local way, but this refactoring is something that I wanted to do since rust-lang/rust#93805 anyway.