proposal: allow documentation editors to order child pages of a book page

From ✨ Allow access to page to order book page's children Needs review :

Many of the documentation pages on d.org could to with rearranging to make the order more logical and comprehensible to readers.

Here is an example: https://drupal.org/documentation/modules/flag. The main documentation page for Flag module has a ton of child pages, which are in no particular order, and really ought to be.

However, changing the order of child pages like this requires all the weights to be set correctly in relation to one another. This requires each page to be edited. It's a slow and tedious job!

What would be much better would be a single admin page with weights for all the child pages.

I am leaving that other issue at the infrastructure queue because I think discussion is needed about adding a new module and security.

I'm filing a new issue here for the documentation team to discuss whether this is desirable from the docs POV.