test: Switch from leaked-handles to wtfnode (#2604)

See my comments at
https://github.com/cdr/code-server/pull/2563#issuecomment-763394741

test/wtfnode.ts

@@ -0,0 +1,19 @@
+import * as wtfnode from "wtfnode"
+
+let active = false
+
+export function setup(): void {
+  if (active) {
+    return
+  }
+  active = true
+
+  const interval = 5000
+  const wtfnodeDump = () => {
+    wtfnode.dump()
+    const t = setTimeout(wtfnodeDump, interval)
+    t.unref()
+  }
+  const t = setTimeout(wtfnodeDump, interval)
+  t.unref()
+}