Ensure post transaction callbacks are only at the end of the root Drupal transaction

All the code changes look good to me.
The added code comments are clear.
For the different situations is testing added.
The testbot is green for all supported databases.
For me it is RTBC.

I read the issue summary and the MR. I did not do a code review, just the comments. I applied my own suggestions for minor grammar fixes. The comments on the whole make sense but I suggested some improvements. And I had a question about comments in the tests. I am going to set this to Needs Work so someone checks the suggestions.

I have added credit as well.

Applied @quietone suggestions, but then changed a bit again as I thought the end result was still not accurate. Not a native speaker, so please bear with me.

@mondrake, thanks for updating the comments. They are much easier to understand now and will benefit those who come after us. Thanks!

I was about to restore the RTBC when I checked the tests. There is a failing test, core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationExistingFileTest.php and I have restarted that set of functional tests. Once tests are passing this can go back to RTBC.

Rebased, tests are green now so back to RTBC per #12.

@quietone your change of the title text does no longer read. Unsure what you meant to change, so leaving as is.

Fixed a typo in a comment, waited for a green test-run - which passed.
Committed to 11.x and backported 11.0.x, 10.4.x and 10.3.x

Thanks folks 🙌

larowlan → closed merge request !7484

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

Wow! What an epic bug and fascinating fix! 👏