Try deferring output buffer processing until shutdown hook

[westonruter]

Summary

This is an alternative approach to #6233 based on @schlessera's idea in #6232 (comment):

Not yet sure whether this is technically possible, but another way to solve this would be to exit the output buffering callback as soon as possible and defer the processing to another method outside of that callback.

What happens if you add another shutdown handler while within the output buffering callback?

See #6232

Checklist

• My code is tested and passes existing tests.
• My code follows the Engineering Guidelines (updates are often made to the guidelines, check it out periodically).

[github-actions]

Plugin builds for 40e1601 are ready 🛎️!

• Download development build
• Download production build