Jco transpile: implementation of wasi-io for Web

[yoshuawuyts]

Tasks

• streams.read
• streams.blocking-read
• streams.skip
• streams.blocking-skip
• streams.subscribe-to-input-stream
• streams.drop-input-stream
• streams.check-write
• streams.write
• streams.blocking-write-and-flush
• streams.flush
• streams.blocking-flush
• streams.subscribe-to-output-stream
• streams.write-zeroes
• streams.splice
• streams.blocking-splice
• streams.forward
• streams.drop-output-stream
• poll.drop-pollable
• poll.poll-oneoff

[vados-cosmonic]

One issue that needs to get cleared up is the reusability of Pollables:

https://github.com/bytecodealliance/jco/blob/main/packages/preview2-shim/lib/browser/io.js#L191

Pollables need to be able to be reused