policy: manifest with subresource integrity checks

This enables code loaded via the module system to be checked for
integrity to ensure the code loaded matches expectations.

PR-URL: https://github.com/nodejs/node/pull/23834


Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Vladimir de Turckheim <vlad2t@hotmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>