Editor: Add Nonce Endpoint

This is a follow up to #47843, implementing a PHP endpoint and inline scripts 
after the editor package updates. The action was originally added in
https://github.com/WordPress/gutenberg/pull/16683.

Fixes #48076.




git-svn-id: https://develop.svn.wordpress.org/trunk@46253 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/admin-ajax.php

@@ -53,6 +53,7 @@ $core_actions_get = array(
 	'autocomplete-user',
 	'dashboard-widgets',
 	'logged-in',
+	'rest-nonce',
 );
 
 $core_actions_post = array(