worker: Add experimental SynchronousWorker implementation
Adds SynchronousWorker from the standalone synchronous-worker module directly into Node.js (as Experimental).
The synchronous-worker module was originally written by Anna Henningsen and is incorporated here at Matteo Collina's request and Anna's permission.
This is near verbatim to the original module with necessary adaptations to match Node.js style.
Signed-off-by: James M Snell jasnell@gmail.com
/cc @addaleax @mcollina