Rollup merge of #92443 - mdibaiee:90703/resolve-traits-of-primitive-types, r=Manishearth

Rollup merge of #92443 - mdibaiee:90703/resolve-traits-of-primitive-types, r=Manishearth

Rustdoc: resolve associated traits for non-generic primitive types

Fixes #90703

This seems to work:
<img width="457" alt="image" src="https://user-images.githubusercontent.com/2807772/147774059-9556ff96-4519-409e-8ed0-c33ecc436171.png">

I'm just afraid I might have missed some cases / broken previous functionality.

I also have not written tests yet, I will have to take a look to see where tests are and how they are structured, but any help there is also appreciated.