src: add embedding helpers to reduce boilerplate code
Provide helpers for a) spinning the event loop and b) setting up and tearing down the objects involved in a single Node.js instance, as they would typically be used. The former helper is also usable inside Node.js itself, for both Worker and main threads.
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines