Cross-publish for javascript

[ryan-williams]

All dependencies of the zarr module are cross-published for JVM and JS except JBlosc.

Cross-publishing to JS would be "nice to have", either for use on the client in #11, and also to prepare for adding a scala-native target later.

Native support is currently blocked on Cats, which in turn needs ScalaCheck, and so is probably a few months out at least, but it would be really cool as a potential way to support R as well, or even be usable from Python, in case features make it in here that aren't in the reference python implementation.