Update Package Manager event documentation in package_manager.api.php

Created 📌 Throw an exception if stopPropagation() called for `PreOperationStageEvent` and no error has been added Fixed because I realized you could easily mess up the validation if you didn't know what you were doing

4 remarks on the MR — but I'm so glad the API docs are getting improved! 😄👍

Getting there … but still a few remarks 😇

Almost ready!

99% done!

Ready to land!

@tedbow: let's land this, so we can finally do 📌 Define the Package Manager API (package_manager.api.php is outdated) Fixed , which this blocks. 🤞

Sorry to kick this back, but there are a few things I'd like to see changed here for clarity's sake. (If you want, I can do the work - just assign it to me.)

Looks good to me!

Made a couple of small fixes-on-commit, will merge when tests pass.

This unblocked #3318306: #3318306-16: Define the Package Manager API (package_manager.api.php is outdated) → .

Automatically closed - issue fixed for 2 weeks with no activity.