n-api: re-write test_make_callback
This re-writes the test in C by dropping std::vector<napi_value> in favour of a C99 variable length array, and by dropping the anonymous namespace in favour of static function declarations.
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
commit message follows commit guidelines