Add private/draft/future/pending pages to parent dropdown in page attributes and Quick Edit

wps_dropdown_pages_args_add_parents.php

<?php

add_filter( 'page_attributes_dropdown_pages_args', 'wps_dropdown_pages_args_add_parents' );
add_filter( 'quick_edit_dropdown_pages_args', 'wps_dropdown_pages_args_add_parents' );
/**
 * Add private/draft/future/pending pages to parent dropdown.
 */
function wps_dropdown_pages_args_add_parents( $dropdown_args, $post = NULL ) {
    $dropdown_args['post_status'] = array( 'publish', 'draft', 'pending', 'future', 'private', );
    return $dropdown_args;
}