feat: Allow navigation targets to be duplicated when the focus range lies in the macro definition site
![Code_KI1EfbAHRZ](https://github.com/rust-lang/rust-analyzer/assets/3757771/2cc82e5c-320f-4de2-9d55-fe975d180f2a)
Basically if a name of an item originates from the macro definition we now point to that as well as the creating macro call.
Big diff because I also made `FileId`s field private due to some debugging I had to do (having a searchable constructor makes things easier).