Replace Apache Arrow JS with Flechette?

[jheer]

The flechette package provides faster and more flexible Arrow parsing than the JS reference implementation. It also provides a (more correct) implementation of the fast row object proxies used by our Arrow loader here. Should we switch out the apache-arrow tableFromIPC for the flechette version?

If so:

• We can simply call flechette's version of tableFromIPC with the useProxy: true option to get fast row proxy objects.
• We can add "duck typing" checks to pass existing tables (from either flechette or arrow-js) through to Vega, calling toArray() on them first to return Vega's desired array-of-objects format.
• We could also consider adding support to pass-in flechette extraction options (like useBigInt, useMap, etc).

@domoritz any thoughts?

[jheer]

I've also added a PR for this: #365