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>

doc/api/report.md

@@ -292,7 +292,8 @@ is provided below for reference.
     {
       "type": "loop",
       "is_active": true,
-      "address": "0x000055fc7b2cb180"
+      "address": "0x000055fc7b2cb180",
+      "loopIdleTimeSeconds": 22644.8
     }
   ],
   "workers": [],

src/node_report.cc

@@ -294,6 +294,10 @@ static void WriteNodeReport(Isolate* isolate,
         static_cast<bool>(uv_loop_alive(env->event_loop())));
     writer.json_keyvalue("address",
         ValueToHexString(reinterpret_cast<int64_t>(env->event_loop())));
+
+    // Report Event loop idle time
+    uint64_t idle_time = uv_metrics_idle_time(env->event_loop());
+    writer.json_keyvalue("loopIdleTimeSeconds", 1.0 * idle_time / 1e9);
     writer.json_end();
   }
 

test/report/test-report-uv-handles.js

@@ -128,6 +128,9 @@ if (process.argv[2] === 'child') {
         assert.strictEqual(handle.filename, expected_filename);
         assert(handle.is_referenced);
       }),
+      loop: common.mustCall(function loop_validator(handle) {
+        assert.strictEqual(typeof handle.loopIdleTimeSeconds, 'number');
+      }),
       pipe: common.mustCallAtLeast(function pipe_validator(handle) {
         assert(handle.is_referenced);
       }),