[WordPress] Include private, draft, and pending posts in parent dropdowns (single post, bulk edit, and quick edit views).

wp-show-all-parents.php

add_filter( 'page_attributes_dropdown_pages_args', 'my_slug_show_all_parents' );
add_filter( 'quick_edit_dropdown_pages_args', 'my_slug_show_all_parents' );
/**
 * Show all parents, regardless of post status.
 *
 * @since   1.0.0
 *
 * @param   array  $args  Original get_pages() $args.
 *
 * @return  array  $args  Args set to also include posts with pending, draft, and private status.
 */
function my_slug_show_all_parents( $args ) {
	$args['post_status'] = array( 'publish', 'pending', 'draft', 'private' );
	return $args;
}