Fix source spans for binding groups - #3462

             v
   6  test = go 10
   7    where
   8    ok :: Int -> Boolean
      ...
  11    go :: int -> Int
  12    go n | ok n = n
  13         | otherwise = go (n - 1)
                                   ^

  Type variable int is undefined.

  while checking the kind of int -> Int
  while checking that expression go 10
                                   where
                                   ok = \$0 ->
                                          (...) 0
                                   go = \n ->
                                          ...
    has type Int
  in value declaration test

This now points to the correct definition, but the source span does not include the offending item. Is it possible to include the type signature in the span, or do we just drop all span relating to type signature?

Edit: I misread this error (not my day apparently). Is it possible to narrow this down to the go definition, or does it necessarily need to include the whole binding group?

@natefaubion I haven't checked yet but I suspect that the combination of this PR and #3463 will narrow the error down to the go declaration.

@LiamGoodacre Do we want to go ahead and merge this as is and make follow-up improvements?

@natefaubion yeah that sounds good.
I've just rebased against master.
Will need an approved review to merge.