process: code cleanup for nextTick

Fix a few edge cases and non-obvious issues with nextTick:
1. Emit destroy hook in a try-finally rather than triggering
it before the callback runs.
2. Re-word comment for processPromiseRejections and make sure
it returns true in the rejectionHandled case too.
3. Small readability improvements.

PR-URL: https://github.com/nodejs/node/pull/28047


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>