Auto suggest ImportQualifiedPost, intelligently suggest LambdaCase and ScopedTypeVariables

[sergv]

The LambdaCase and ScopedTypeVariables extensions are typically not suggested by ghc in the form e.g. did you mean to enable LambdaCase so just looknig for extension name in the error message is not sufficient.

The plan is to enable LambdaCase if ghc failed to parse a case expression and user actually used lambda case by typing \case. For ScopedTypeVariables the error message is more direct but still doesn't mention ScopedTypeVariables directly.