Bifoldable instance for Map

I'd like to propose a change to the containers package: adding a Bifoldable instance to Map. I briefly mentioned this on Reddit [1] and no obvious problems were brought up. I submitted a PR implementing it [2]. This seems like an obvious and straightforward instance to me. Thoughts? Joseph C. Sible [1]: https://old.reddit.com/r/haskell/comments/fsgqd6/monthly_hask_anything_april... [2]: https://github.com/haskell/containers/pull/714