benchmark,lib: add process.hrtime.bigint benchmark

Add a benchmark, and amend the relevant source code comment to state
that currently, switching to directly returning a BigInt is not
stopped by technical obstacles but rather the fact that using a typed
array is actually a bit faster (about 2.5 %, measured locally).

PR-URL: https://github.com/nodejs/node/pull/26381


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>