Added a unit test for testing the memory usage of readFileSync.
Test is looking specifically for the the issue caused by failing
to free the filepath buffer in fs::ReadFileUtf8(), but it will also
catch other significant memory leaks in readFileSync() as well.
Refs: https://github.com/nodejs/node/issues/57800
PR-URL: https://github.com/nodejs/node/pull/57811
Fixes: https://github.com/nodejs/node/issues/57800
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
