Customize: Prevent dropping backslashes from input on general settings and settings for nav menus and some widgets.

Ensures that intentional backslashes (e.g. "\o/") can be used in:

* Site title
* Site description
* Nav menu name
* Custom Menu widget title
* Tag Cloud widget title
* Text widget body if can't `unfiltered_html`

The latter three are also fixed on the widgets admin page.

Fixes #35898.


git-svn-id: https://develop.svn.wordpress.org/trunk@36622 602fd350-edb4-49c9-b593-d223f7449a82

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

@@ -496,7 +496,6 @@ class WP_Customize_Setting {
 	 * @return string|array|null Null if an input isn't valid, otherwise the sanitized value.
 	 */
 	public function sanitize( $value ) {
-		$value = wp_unslash( $value );
 
 		/**
 		 * Filter a Customize setting value in un-slashed form.