Should monoidal-containers split into lens and these subpackages?

[emilypi]

Related to #73 is the idea that monoidal-containers should not bring in the these (lower dep footprint) or lens (higher dep footprint) universes. Rather, it would be nice to punt them to subpackages like these-lens so that the underlying core newtypes + api can be used in other packages without having to inherit the footprint. I would like to build upon this library if possible, but lens is a non-starter my project. It would make #73 much cleaner as well.

Thoughts?

[endgame]

Modern versions of these have a very tiny dep footprint, so you'd be defining instances on classes provided by semialign. Which doesn't have a particularly large dep footprint either now that indexed-traversable exists. I have no objection to lens in my projects, but I think a separate package that exports instances for things in large-footprint packages like lens is probably a good idea.

I mean, the better idea is to go back in time and put the good Monoid instances into containers.

[adamgundry]

I would also like to see lens instances moved to a separate package. (I tripped over this by trying to compile ghc-debug-brick and wondering why it was pulling in no fewer than two lens libraries...)