Rollup merge of #108584 - GuillaumeGomez:rustdoc-search-background, r=notriddle

Put backtick content from rustdoc search errors into a <code> elements

Some screenshots of the result:

![Screenshot from 2023-02-28 22-37-09](https://user-images.githubusercontent.com/3050060/221990290-fa84f1cf-5a64-4ce5-8433-ee36cedf4c00.png)
![Screenshot from 2023-02-28 22-36-59](https://user-images.githubusercontent.com/3050060/221990298-f8177eeb-894b-4fce-a6fc-06d17c8b7ca2.png)
![Screenshot from 2023-02-28 22-36-51](https://user-images.githubusercontent.com/3050060/221990301-41bffd64-d041-41f1-995a-983925b1fbb1.png)

You can test it [here](https://rustdoc.crud.net/imperio/rustdoc-search-background/foo/index.html?search=%22).

r? ```@notriddle```

Author: matthiaskrgr