Customize: Ensure `textarea` for Custom CSS displays as code (in LTR) when an RTL language is active.

Merges [39499] onto 4.7 branch.
Fixes #39085 for 4.7.


git-svn-id: https://develop.svn.wordpress.org/branches/4.7@39500 602fd350-edb4-49c9-b593-d223f7449a82

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

@@ -4128,6 +4128,9 @@ final class WP_Customize_Manager {
 			'type'     => 'textarea',
 			'section'  => 'custom_css',
 			'settings' => array( 'default' => $custom_css_setting->id ),
+			'input_attrs' => array(
+				'class' => 'code', // Ensures contents displayed as LTR instead of RTL.
+			),
 		) );
 	}