Create event listeners to validate stage packages
Problem/Motivation
In #3225099: Change Readiness checker services to event subscribers to allow checking at different stages we added events for different points in the update cycle including pre-commit
I briefly took the logic out of `\Drupal\automatic_updates\Updater::validateStaged() and moved it to it's own event listener.
To make that issue smaller I deleted that listener for this follow up
The code in validateStaged() was not great and deserves it's own issue anyways.
Proposed resolution
Start by reversing this commit https://git.drupalcode.org/sandbox/tedbow-3222651/-/merge_requests/4/diffs?commit_id=3a49d61a6860a28b453f9470b40266f5b1d5a02d
Remaining tasks
User interface changes
API changes
Data model changes
Related issue: Issue #3225099
Edited by drupalbot