Suggestions or actions to use type synonyms

It would perhaps be nice if HLS suggested using in scope type synonyms sometimes.

To make an example using the `hnix` package: if I use the excellent code action `Define funArity :: Fix (Compose (Ann SrcSpan) NExprF) -> Int` I end up with the unhuman given type sig, when `funArity :: NExprLoc -> Int` would be much nicer.

It's probably quite hard to come up with the perfect rule here, but how do people feel about a heuristic along the lines of:

- The sig is in scope
- The types are equal
- Using the synonym is much shorter

(Better but more difficult would be to calculate the preference in existing code (user and library) between the synonym and the expanded version)