Make Arbitrary instance of Integer able to generate large numbers out of the box

There is a slight problem with Arbitrary instance of Integer, namely that it won't generate large numbers (by which I mean numbers that don't fit into Int64) by default, which makes it impossible to test all the code paths out of the box as it is not uncommon for the code that deals with Integers distinguish between small and large numbers (which makes sense even given its constructors: https://hackage.haskell.org/package/integer-gmp-1.0.1.0/docs/src/GHC.Integer.Type.html#Integer).

Can current instance be replaced with something along the lines of

instance Arbitrary Integer where
    arbitrary = sized $ \sz -> do
        n <- choose (1, sz)
        sign <- arbitrary
        (if sign then negate else id) . foldr f 0
            <$> replicateM n arbitrary
      where
        f :: Word8 -> Integer -> Integer
        f w acc = (acc `shiftL` 8) + fromIntegral w

?

As of now defining a newtype LargeInteger = LargeInteger Integer with appropriate Arbitrary instance is somewhat of a workaround, but there are two problems with that:

1. You need to remember to do that.
2. Sometimes it's impossible/inconvenient to use it, e.g. when we're testing a data type with fields of type Integer (or better yet, where Integer is nested somewhere deep within tested data type).

Start at the current Arbitrary Integer instance and compare its behavior with the proposed size-based generation. Add coverage demonstrating that values larger than Int64 can be generated by default, then run the relevant QuickCheck tests and confirm existing Integer generation remains valid.