inspector: track async stacks when necessary

With this change, we do async stack tracking only when explicitly
requested by the inspector client. This avoids unnecessary overhead
for clients that might not be interested in async stack traces.

PR-URL: https://github.com/nodejs/node/pull/16308
Fixes: https://github.com/nodejs/node/issues/16180


Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>