Add for await of

[trossimel-sc]

Summary

This PR introduces support for the for await of syntax through IR. In detail:

• The helper function _makeAsyncIterator is used to create an async iterator for a given iterable. It checks if an async iterator method is available; if not, it creates an async iterator from a synchronous iterator by wrapping its results in promises.
• Added a genAsyncForOfStatement which handles the for await of loop by iterating over the async iterator object. It follows the same rules described here

Test Plan

• Added 3 unit tests to cover the main behavior of for await of loop

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