Customize: Allow page stubs to be created via dropdown-pages controls in the Static Front Page section.

This ability was previously added to nav menus via the available page items panel. The "Add New Page" button only appears when the `allow_addition` control param is supplied as `true`. Code is adapted from the Customize Posts feature plugin.

Props celloexpressions, westonruter.
See #38013, #34923.
Fixes #38164.


git-svn-id: https://develop.svn.wordpress.org/trunk@38906 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-customize-manager.php

@@ -3356,6 +3356,7 @@ final class WP_Customize_Manager {
 			'label' => __( 'Front page' ),
 			'section' => 'static_front_page',
 			'type' => 'dropdown-pages',
+			'allow_addition' => true,
 		) );
 
 		$this->add_setting( 'page_for_posts', array(
@@ -3367,6 +3368,7 @@ final class WP_Customize_Manager {
 			'label' => __( 'Posts page' ),
 			'section' => 'static_front_page',
 			'type' => 'dropdown-pages',
+			'allow_addition' => true,
 		) );
 
 		/* Custom CSS */