Delivery API: Fix not reindexing branch descendants when branch root already published but unchanged (closes #20370)

[Migaroez]

Description

Fixes #20370

Testing

Follow the steps in the linked issue OR

• Enable the delivery api
• Create a tree structure of saved but not published nodes trough the backoffice
• Publish the root node
• Use Publish with descendants (check include unpublished nodes) on the root node
• Check the delivery api index (as described in the linked issue)

[AndyButland]

Can confirm this works in local testing. Previously an unpublished node would remain with published = "n" in the next even when the parent was published with unpublished children. With this update I see it's fixed with published = "y".

Maybe you could just try to clarify the comment you've added on lines 64-65 as I find it a bit hard to follow? Just to help someone coming to this in future and seeing this code fragment.

After that, happy for you to merge. You should then merge main to v17/dev and then cherry-pick this into release/17.0. The issue can then be labelled with release/16.4 and release/17.0.

[kjac]

@Migaroez code looks good 👍 but it also feels like something that can become volatile moving forward. Is there any chance I could trouble you for an integration test that proves the fix?