Rollup merge of #98671 - GuillaumeGomez:source-sidebar-fixes, r=notriddle

Rollup merge of #98671 - GuillaumeGomez:source-sidebar-fixes, r=notriddle

Fix source sidebar bugs

This PR fixes the following two bugs:

![Screenshot from 2022-06-29 14-39-58](https://user-images.githubusercontent.com/3050060/176449070-3e3762da-2bfe-4acf-8eb0-34f6eb4c94ed.png)
![Screenshot from 2022-06-29 15-05-09](https://user-images.githubusercontent.com/3050060/176449073-b164820b-bd71-4b1a-990c-bba4e5fce196.png)

I added regression tests to prevent them to happen again.

I think we should backport it to beta as well.

You can test it [here](https://rustdoc.crud.net/imperio/source-sidebar-fixes/src/std/lib.rs.html).

cc ```@jsha```
r? ```@notriddle```