test: add test cases for validateOffsetLengthWrite.
Summary.
Added some test cases for validateOffsetLengthWrite in lib/internal/utils.js
This PR improves the test coverage of it. https://coverage.nodejs.org/coverage-75e91659887012f7/root/internal/fs/utils.js.html#L301
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