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ARROW-2779: [JS] stream reader fixes

This is a stop-gap fix for node-stream compatibility. Some APIs (like node's `http` module) still only accept Buffer instances, so this PR emits those if we're in node. Also includes a small fix in `fromReadableStream` to ensure it doesn't try to read the length if there's not enough bytes.

Author: ptaylor <paul.e.taylor@me.com>

Closes #2201 from trxcllnt/js-stream-reader-fixes and squashes the following commits:

d229a558 <ptaylor> Merge branch 'master' into js-stream-reader-fixes
2c2e6949 <ptaylor> emit native Buffers in node, else Uint8Arrays
ab02407f <ptaylor> silence node's experimental async-iterator warnings
f4835672 <ptaylor> Merge branch 'js-stream-reader-fixes' of github.com:trxcllnt/arrow into js-stream-reader-fixes
34251043 <ptaylor> Update dependencies
481d15aa <ptaylor> guard against reading data from 0-length buffer
d4118712 <ptaylor> guard against reading data from 0-length buffer
9b199c39 <ptaylor> finish implementing unions in the JS reader
953232c0 <ptaylor> write schema metadata