Add upstream

wp-content/plugins/jetpack/modules/theme-tools/js/suggest.js

@@ -0,0 +1,7 @@
+/* global ajaxurl:true */
+jQuery( function( $ ) {
+	$( '#customize-control-featured-content-tag-name input' ).suggest(
+		ajaxurl + '?action=ajax-tag-search&tax=post_tag',
+		{ delay: 500, minchars: 2 }
+	);
+} );