Auto merge of #88469 - patrick-gu:master, r=dtolnay

Auto merge of #88469 - patrick-gu:master, r=dtolnay

Add links in docs for some primitive types

This pull request adds additional links in existing documentation of some of the primitive types.

Where items are linked only once, I have used the `[link](destination)` format. For items in `std`, I have linked directly to the HTML, since although the primitives are in `core`, they are not displayed on `core` documentation. I was unsure of what length I should keep lines of documentation to, so I tried to keep them within reason.

Additionally, I have avoided excessively linking to keywords like `self` when they are not relevant to the documentation. I can add these links if it would be an improvement.

I hope this can improve Rust. Please let me know if there's anything I did wrong!