Add code-action to turn derived type-class into its implementation

E.g. for a code-snippet

```haskell
data Bar = Bar deriving (Show)
```

I would like to be able to generate roughly what this `deriving` desugars to.
Ideally, (don't know about the specifics) only the implementation that are not default, e.g.

```haskell
data Bar = Bar

instance Show Bar where 
  show Bar = "Bar"
```