Hidden subpages of a tree template are not marked as visible upon creation of a document from that template, as opposed to the root page

How to reproduce:

• create a template with a root page and some subpages (other than WebPreferences pages) - using the feature added by XWIKI-12775
• mark all the pages in the template tree as hidden, to have them excluded from search and document listing
• create a template provider that serves this template
• create a document from that template

Expected result:

• the template root and its child pages are copied, all marked as non hidden, included as visible in the wiki content

Actual result:

• the template root page is copied as visible, but all child pages remain hidden, as they were in the original template

Note: probably not all pages will need to become visible: the WebPreferences pages, which may be a very frequent case of subpage, will probably need to stay hidden since they are technical pages.
Also, for the rest of the pages in the template, there can be a debate about whether they should become visible or not, just like there can be one for the root page of the template ( see XWIKI-13554 ) but I would say if i'd have to chose a default, I would chose to do the same as the root page, that is make them visible.