src: add loop idle time in diagnostic report

Add libuv's cumulative idle time in the diagnostic report.
Add the data under the libuv's loop section

Refs: https://github.com/nodejs/node/pull/34938
PR-URL: https://github.com/nodejs/node/pull/35940


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>