src: replace var for (let|const) in utilities module

Update Utilities module to replace var for let or const

PR-URL: https://github.com/nodejs/node/pull/18814


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Matheus Marchini <matheus@sthima.com>