Merge #1797

Merge #1797

1797: Use VSCode fs API's in extension r=matklad a=LDSpits

This will close #1670.

I've replaced the `CargoWatcher`s `Cargo.toml` check with a version that uses the `fs` API of vscode.

While making this I've identified an issue with the detection of the `cargo.toml`, we can only load projects where the cargo.toml is in the root of the workspace. but that's a separate issue 😄

Co-authored-by: Lucas Spits <spits.lucas@gmail.com>