Refactor SuggestExtension constructor in GhcHint

This commit refactors the SuggestExtension type constructor of the GhcHint to be more powerful and flexible. In particular, we can now embed extra user information (essentially "sugar") to help clarifying the suggestion. This makes the following possible:

Suggested fix: Perhaps you intended to use GADTs
               or a similar language extension to enable syntax: data T where

We can still give to IDEs and tools a LangExt.Extension they can use, but in the pretty-printed message we can tell the user a bit more on why such extension is needed.

On top of that, we now have the ability to express conjunctions and disjunctions, for those cases where GHC suggests to enable "X or Y" and for the cases where we need "X and Y".