avoid redundant toList-calls in containers package

[jvoigtlaender]

In the spirit of #1569, various toList calls could be optimized away. But I'm not sure containers is "in scope" since no other rules currently seem to refer to functions from it.

Anyway, here are the proposed rules:

    - warn: {lhs: foldMap f (Data.IntMap.toList x), rhs: Data.IntMap.foldMapWithKey (curry f) x}
    - warn: {lhs: foldr f z (Data.IntMap.toList x), rhs: Data.IntMap.foldrWithKey (curry f) z x}
    - warn: {lhs: foldr' f z (Data.IntMap.toList x), rhs: Data.IntMap.foldrWithKey' (curry f) z x}
    - warn: {lhs: foldl f z (Data.IntMap.toList x), rhs: Data.IntMap.foldlWithKey (curry . f) z x}
    - warn: {lhs: foldl' f z (Data.IntMap.toList x), rhs: Data.IntMap.foldlWithKey' (curry . f) z x}
    - warn: {lhs: null (Data.IntMap.toList x), rhs: Data.IntMap.null x}
    - warn: {lhs: length (Data.IntMap.toList x), rhs: Data.IntMap.size x}

    - warn: {lhs: foldr f z (Data.IntSet.toList x), rhs: Data.IntSet.foldr f z x}
    - warn: {lhs: foldr' f z (Data.IntSet.toList x), rhs: Data.IntSet.foldr' f z x}
    - warn: {lhs: foldl f z (Data.IntSet.toList x), rhs: Data.IntSet.foldl f z x}
    - warn: {lhs: foldl' f z (Data.IntSet.toList x), rhs: Data.IntSet.foldl' f z x}
    - warn: {lhs: null (Data.IntSet.toList x), rhs: Data.IntSet.null x}
    - warn: {lhs: length (Data.IntSet.toList x), rhs: Data.IntSet.size x}
    - warn: {lhs: elem y (Data.IntSet.toList x), rhs: Data.IntSet.member y x}
    - warn: {lhs: notElem y (Data.IntSet.toList x), rhs: Data.IntSet.notMember y x}

    - warn: {lhs: foldMap f (Data.Map.toList x), rhs: Data.Map.foldMapWithKey (curry f) x}
    - warn: {lhs: foldr f z (Data.Map.toList x), rhs: Data.Map.foldrWithKey (curry f) z x}
    - warn: {lhs: foldr' f z (Data.Map.toList x), rhs: Data.Map.foldrWithKey' (curry f) z x}
    - warn: {lhs: foldl f z (Data.Map.toList x), rhs: Data.Map.foldlWithKey (curry . f) z x}
    - warn: {lhs: foldl' f z (Data.Map.toList x), rhs: Data.Map.foldlWithKey' (curry . f) z x}
    - warn: {lhs: null (Data.Map.toList x), rhs: Data.Map.null x}
    - warn: {lhs: length (Data.Map.toList x), rhs: Data.Map.size x}

Similar optimizations would likely also be possible regarding toList from the aeson, vector and unordered-containers packages.

[jvoigtlaender]

See also #1620 for more hints that could be added here as well.