Fix Drupal.Commenting.FunctionComment.Missing in Kernel tests

Raised MR !11284. Kindly review

Tagging, so it shows up on the right list

Did a light review but think this needs another once over before fully going into review.

Made changes as per review comments in MR

I had some comments, only the first and the last really need action, I could be convinced about the other ones that it does make sense to document it like this.

@borisson_ made change as per one comment and for the other one, added reply in MR. Kindly check. Thanks for the review

There's a couple of open issues still and I think it also needs a reroll.