Add Support For Showing Rust Code Under The Tests Folder

[AtropineTears]

Hi,

I noticed when I create tests under the tests folder I am not allowed to see the helpful information that is in your extension. Can you add this feature?

[lnicola]

I'm not sure what's not working here, but can you give https://marketplace.visualstudio.com/items?itemName=matklad.rust-analyzer a try?