src: munmap(2) upon class instance destructor

Replace `OnScopeLeave` with a class whose instance destructor performs
the munmap(2).

Signed-off-by: Gabriel Schulhof <gabriel.schulhof@intel.com>
Fixes: https://github.com/nodejs/node/issues/32532
PR-URL: https://github.com/nodejs/node/pull/32570


Co-Authored-By: Anna Henningsen <github@addaleax.net>
Co-Authored-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>