Reimplement Zip Operator Using Lift

- Use new lift operator implement and non-blocking synchronization approach.
- I have had the concurrency model reviewed by some colleagues and all unit tests are passing but further review is justified and welcome.
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OperatorZipIterable
Zip NULL and COMPLETE Sentinels
Merge pull request #785 from benjchristensen/operator-zip

Reimplement Zip Operator Using Lift [Preview]