util: add boxed BigInt formatting to util.inspect

Before:

> Object(7n)
BigInt {}

After:

> Object(7n)
[BigInt: 7n]

PR-URL: https://github.com/nodejs/node/pull/19341


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>