Merge #11869

11869: fix: code blocks with tilde also works like code block r=Veykril a=moreal

The `rustdoc` uses the `pulldown_cmark` package to parse *doc_comment* and the package also treat triple `~` characters also as code block fences. So when we run `cargo doc`, they will be placed also.

<img width="965" alt="image" src="https://user-images.githubusercontent.com/26626194/161208072-5a09a209-57fc-4a52-b190-b0a9be9ffcd6.png">

But `rust-analyzer` doesn't support it so it doesn't have any injected code highlights and any `Run doctest` hint. This pull request tries to allow also them. 🙇🏻‍♂️

Before:

<img width="224" alt="image" src="https://user-images.githubusercontent.com/26626194/161207405-b1d6cfda-82b1-4f60-8e42-c51d0ed98f38.png">

After:

<img width="161" alt="image" src="https://user-images.githubusercontent.com/26626194/161207693-8e39997c-9ca6-4e69-8c65-e9b70899f7db.png">

Co-authored-by: Lee Dogeon <dev.moreal@gmail.com>