`mapWithIndex` should reuse `Data.FunctorWithIndex.mapWithIndexArray`

[JordanMartinez]

This library defines the monomorphic mapWithIndex function as a zipWith function on the initial array and an indices-array constructed using the input array's size. I'd guess it's actually slower than just using FunctorWithIndex.mapWithindex.

The actual monomorphic and dictionary-less mapWithIndex FFI is defined in foldable-traversable via mapWithIndexArray. Perhaps the mapWithIndexArray could be exported in FunctorWithIndex, such that we can re-export here under the name mapWithIndex?

[natefaubion]

I think the FFI implementation needs to move here because foldable-traversable depends on arrays.

Edit: I take that back, it does not depend on arrays. Arrays depends on foldable-traversable.

[natefaubion]

I think that exporting a monomorphic version that's just an alias of the dictionary version would have identical performance characteristics because it would be partially applied.

[JordanMartinez]

Works for me.