Allow users with access to unpublished nodes to create unpublished books

Problem/Motivation

It is currently not possible to create unpublished book pages as children of another unpublished node page: unpublished pages do not appear in the Parent combo of the node creation page. That would be useful if I want to create a book but not publish it immediately.

To reproduce the problem:
1) Install a fresh Drupal 8, enable book module
2) Add a book node -> set title as "Front Page" -> edit the book outline -> select "create a new book" -> save
3) Add a book node -> set title as "Chapter 1" -> edit the book outline -> select "Front Page" as parent item
4) Add a book node -> set title as "chapter 2" -> edit the book outline -> select "Front Page" as parent item
5) Add a book node -> set title as "Page 1" -> edit the book outline -> select "Chapter 1" as parent item
6) Add a book node -> set title as "Page 2" -> edit the book outline -> select "Chapter 2" as parent item
7) Unpublish the Front page.
8) Edit "Chapter 1" book node, in book outline, book name and parent item become empty
9) Edit "Page 1" book node, in book outline, book name and parent item become empty
10) Publish "Front Page" again
11) Go to edit page of "Chapter 1" book node, in book outline, book name and parent item is good now
12) Edit "Page 1" book node, in book outline, book name and parent item is good now
13) Unpublish "Chapter 1" book node
14) Edit "Page 1" book node, in book outline, parent item have been changed from "Chapter 1" to "Front Page"

Proposed resolution

The Entity Query alone is sufficient to check access, so the explicit status condition can be removed.

Remaining tasks

Review.

Beta phase evaluation