Merge #1408

Merge #1408

1408: Associated type basics & Deref support r=matklad a=flodiebold

This adds the necessary Chalk integration to handle associated types and uses it to implement support for `Deref` in the `*` operator and autoderef; so e.g. dot completions through an `Arc` work now.

It doesn't yet implement resolution of associated types in paths, though. Also, there's a big FIXME about handling variables in the solution we get from Chalk correctly.

Co-authored-by: Florian Diebold <flodiebold@gmail.com>