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lib: make AbortSignal cloneable/transferable

Rodrigo Muino Tomonari requested to merge github/fork/jasnell/transferable-abortsignal into master

Refs: https://github.com/whatwg/dom/issues/948

Allows for using AbortSignal across worker threads and contexts.

const ac = new AbortController();
const mc = new MessageChannel();
mc.port1.onmessage = ({ data }) => {
  data.addEventListener('abort', () => {
    console.log('aborted!');
  });
};
mc.port2.postMessage(ac.signal, [ac.signal]);

Having to include the AbortSignal in the transfer list here is a side effect of our current implementation. We use js_transferable under the covers and use a pair of MessagePorts to communicate between the two AbortSignals. Using [kClone](), there's no way for us to specify that the MessagePort should be included in the transfer list as the [kTransferList] method is not called when using [kClone](). So, we end up having to use [kTransfer]() which requires that the AbortSignal be included in the transfer list. (/cc @addaleax)

/cc @benjamingr

Signed-off-by: James M Snell jasnell@gmail.com

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