util: add type check functions for BigInt arrays

Adds `isBigInt64Array` and `isBigUint64Array`.

PR-URL: https://github.com/nodejs/node/pull/19201


Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>