doc: modified docs to reflect how to invoke gc on Wrapping C++ objects
Currently the documentation for Wrapping C++ Objects doesn't explain how to destruct an object by explicitly invoking the garbage collector. This commit includes a modification to docs that explains how to force the garbage collector to clear objects using V8's command line flags.
Fixes: https://github.com/nodejs/node/issues/19876
Checklist
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documentation is changed or added -
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